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Sync settings

Choose what your account keeps in step on every device where you are signed in.

  • My tools

    Always synced: the tools on your board, their order and size.

  • The windows open on your start page, including what you typed in them.

  • Every note in the notepad – on the notepad page, on your board and in windows.

  • Every list of website shortcuts – on the shortcuts page, on your board and in windows.

  • Every grid in the cover grid maker – on its page, on your board and in windows.

  • Every list of bookmarked organisations in the OIN lookup – on its page, on your board and in windows.

  • Keeps your pipeline and saved recipes on all your devices. Your files are never synced – only the steps and settings.

Turning something off removes it from your account straight away. Your devices keep their own copy.

Notifications

Tools that can tell you about something new while a Synsi tab is open, even when you are in another tab or app. Choose them for this browser.

This browser cannot show notifications from websites.
Notifications are blocked for this site. Allow them in your browser’s site settings (the icon left of the address), then switch them on here.

  • Says “New message” while a Synsi tab is open – never who wrote it or what.

Your choice is stored in this browser only. Notifications never show personal content such as a message or a number. They work while a Synsi tab is open; closed tabs get none.

Browse all tools →

API documentation

All server-capable tools are available through a simple JSON REST API. Anonymous use is rate limited; request an API key for higher limits.

Base URL

https://synsi.nl/api/v1

Authentication

Anonymous requests are allowed with a limit of 20 requests per minute per IP address. With an API key you get a higher limit; send it as a Bearer token:

Authorization: Bearer YOUR_API_KEY

Rate limits

Every response contains X-RateLimit-Limit and X-RateLimit-Remaining headers. When you exceed the limit you receive HTTP 429 with a Retry-After header.

Errors

Errors use HTTP status codes and a consistent JSON body. Validation errors return 422 with the invalid fields:

{
    "error": {
        "code": "validation_failed",
        "message": "The text field must be present.",
        "fields": {
            "text": [
                "The text field must be present."
            ]
        }
    }
}

OpenAPI specification

A machine-readable OpenAPI 3.1 specification is available at: https://synsi.nl/api/v1/openapi.json

Endpoints

Word Counter

Free online word counter: instantly count words, characters (with and without spaces), sentences, paragraphs and reading time. Private, no sign-up.

POST https://synsi.nl/api/v1/tools/word-counter

Parameters

Parameter Type Required Description
text string yes The text to analyse.

Example request

curl -X POST https://synsi.nl/api/v1/tools/word-counter \
  -H "Content-Type: application/json" \
  -d '{"text":"Hello world. How are you?"}'

Example response

{
    "data": {
        "characters": 25,
        "characters_no_spaces": 21,
        "words": 5,
        "sentences": 2,
        "paragraphs": 1,
        "lines": 1,
        "reading_time_seconds": 2,
        "speaking_time_seconds": 2
    },
    "meta": {
        "tool": "word-counter"
    }
}

Case Converter

Convert text to UPPERCASE, lowercase, Title Case, Sentence case, camelCase, snake_case or kebab-case instantly. Free online case converter, no sign-up.

POST https://synsi.nl/api/v1/tools/case-converter

Parameters

Parameter Type Required Description
text string yes The text to convert.
mode string no Target case.
upper · lower · title · sentence · camel · pascal · snake · kebab · constant · alternating · inverse
default: upper

Example request

curl -X POST https://synsi.nl/api/v1/tools/case-converter \
  -H "Content-Type: application/json" \
  -d '{"text":"hello world"}'

Example response

{
    "data": {
        "result": "HELLO WORLD"
    },
    "meta": {
        "tool": "case-converter"
    }
}

Slug Generator

Turn any title into a clean, SEO-friendly URL slug. Removes accents and special characters, lowercase, hyphens or underscores. Free online slug generator.

POST https://synsi.nl/api/v1/tools/slug-generator

Parameters

Parameter Type Required Description
text string yes Text to turn into a URL slug.
separator string no Word separator.
- · _
default: -
lowercase boolean no Convert to lowercase.
default: true

Example request

curl -X POST https://synsi.nl/api/v1/tools/slug-generator \
  -H "Content-Type: application/json" \
  -d '{"text":"Hello World, Café!"}'

Example response

{
    "data": {
        "result": "hello-world-cafe"
    },
    "meta": {
        "tool": "slug-generator"
    }
}

Remove Duplicate Lines

Remove duplicate lines from any list or text instantly. Options for case sensitivity, trimming spaces and removing empty lines. Free, private, no upload.

POST https://synsi.nl/api/v1/tools/remove-duplicate-lines

Parameters

Parameter Type Required Description
text string yes Text with one item per line.
case_sensitive boolean no Treat "Apple" and "apple" as different lines.
default: true
trim boolean no Ignore leading/trailing whitespace when comparing.
default: true
remove_empty boolean no Remove empty lines.
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/remove-duplicate-lines \
  -H "Content-Type: application/json" \
  -d '{"text":"apple\nbanana\napple"}'

Example response

{
    "data": {
        "result": "apple\nbanana",
        "total_lines": 3,
        "unique_lines": 2,
        "removed": 1
    },
    "meta": {
        "tool": "remove-duplicate-lines"
    }
}

Sort Lines

Sort lines of text alphabetically (A–Z or Z–A), numerically, by length or reverse their order. Free online line sorter that runs in your browser.

POST https://synsi.nl/api/v1/tools/sort-lines

Parameters

Parameter Type Required Description
text string yes Text with one item per line.
order string no Sort order.
alpha_asc · alpha_desc · numeric_asc · numeric_desc · length_asc · length_desc · reverse
default: alpha_asc
case_sensitive boolean no Case-sensitive alphabetical sorting.
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/sort-lines \
  -H "Content-Type: application/json" \
  -d '{"text":"banana\napple\ncherry"}'

Example response

{
    "data": {
        "result": "apple\nbanana\ncherry"
    },
    "meta": {
        "tool": "sort-lines"
    }
}

Lorem Ipsum Generator

Generate lorem ipsum placeholder text by paragraphs, sentences or words. Copy or download dummy text for mockups, templates and layouts. Free.

POST https://synsi.nl/api/v1/tools/lorem-ipsum

Parameters

Parameter Type Required Description
count integer no How many units to generate.
default: 3
unit string no
paragraphs · sentences · words
default: paragraphs
start_with_lorem boolean no Start with "Lorem ipsum dolor sit amet...".
default: true

Example request

curl -X POST https://synsi.nl/api/v1/tools/lorem-ipsum \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "result": "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut, labore et dolore magna aliqua enim. Ad minim veniam quis nostrud exercitation. Ullamco laboris nisi aliquip ex, ea commodo consequat duis aute.\n\nIrure in reprehenderit voluptate velit esse cillum, eu fugiat nulla pariatur excepteur sint occaecat. Cupidatat non proident sunt, culpa qui officia deserunt mollit. Anim id est laborum praesent mauris fusce. Nec tellus dapibus diam lorem, ipsum dolor sit amet consectetur adipiscing. Elit sed do eiusmod tempor incididunt, ut labore et dolore magna aliqua enim.\n\nAd minim veniam quis nostrud. Exercitation ullamco laboris nisi aliquip ex ea commodo. Consequat duis aute irure in reprehenderit, voluptate velit esse cillum eu fugiat."
    },
    "meta": {
        "tool": "lorem-ipsum"
    }
}

Reverse Text

Reverse text online: write backwards letter by letter, reverse the word order or flip the order of lines. Works with emoji and accents. Free.

POST https://synsi.nl/api/v1/tools/text-reverser

Parameters

Parameter Type Required Description
text string yes Text to reverse.
mode string no What to reverse.
characters · words · lines
default: characters

Example request

curl -X POST https://synsi.nl/api/v1/tools/text-reverser \
  -H "Content-Type: application/json" \
  -d '{"text":"Hello world"}'

Example response

{
    "data": {
        "result": "dlrow olleH"
    },
    "meta": {
        "tool": "text-reverser"
    }
}

Base64 Encode & Decode

Encode text to Base64 or decode Base64 to text online. Full UTF-8 support and URL-safe Base64URL option. Free, instant and private. Also via API.

POST https://synsi.nl/api/v1/tools/base64

Parameters

Parameter Type Required Description
text string yes Text to encode, or Base64 to decode (UTF-8).
mode string no
encode · decode
default: encode
url_safe boolean no Use the URL-safe alphabet (- and _ instead of + and /, no padding).
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/base64 \
  -H "Content-Type: application/json" \
  -d '{"text":"Hello world"}'

Example response

{
    "data": {
        "result": "SGVsbG8gd29ybGQ="
    },
    "meta": {
        "tool": "base64"
    }
}

URL Encode & Decode

Percent-encode text for safe use in URLs and query strings, or decode encoded URLs back to readable text. UTF-8 support. Free online URL encoder.

POST https://synsi.nl/api/v1/tools/url-encoder

Parameters

Parameter Type Required Description
text string yes Text to encode or decode.
mode string no
encode · decode
default: encode
plus_as_space boolean no Decode "+" as a space (HTML form encoding).
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/url-encoder \
  -H "Content-Type: application/json" \
  -d '{"text":"a b&c=d/é"}'

Example response

{
    "data": {
        "result": "a%20b%26c%3Dd%2F%C3%A9"
    },
    "meta": {
        "tool": "url-encoder"
    }
}

JSON Formatter & Validator

Format, beautify, minify and validate JSON online. Choose 2 spaces, 4 spaces or tabs, and get clear error messages for invalid JSON. Free and private.

POST https://synsi.nl/api/v1/tools/json-formatter

Parameters

Parameter Type Required Description
json string yes JSON document.
mode string no
format · minify · validate
default: format
indent string no Indentation when formatting.
2 · 4 · tab
default: 2

Example request

curl -X POST https://synsi.nl/api/v1/tools/json-formatter \
  -H "Content-Type: application/json" \
  -d '{"json":"{\"name\":\"synsi\",\"tools\":[1,2,3]}"}'

Example response

{
    "data": {
        "result": "{\n  \"name\": \"synsi\",\n  \"tools\": [\n    1,\n    2,\n    3\n  ]\n}"
    },
    "meta": {
        "tool": "json-formatter"
    }
}

Social Media Preview

Preview how a page link may look in a social post. Check its Open Graph and Twitter Card title, description and image.

POST https://synsi.nl/api/v1/tools/social-graph-viewer

Parameters

Parameter Type Required Description
url string yes Public HTTP or HTTPS page URL to inspect.

Example request

curl -X POST https://synsi.nl/api/v1/tools/social-graph-viewer \
  -H "Content-Type: application/json" \
  -d '{"url":"https://example.com/article"}'

Hash Generator

Generate MD5, SHA-1, SHA-256, SHA-384 and SHA-512 hashes of any text instantly. UTF-8 input, uppercase option, runs in your browser. Also via API.

POST https://synsi.nl/api/v1/tools/hash-generator

Parameters

Parameter Type Required Description
text string yes Text to hash (UTF-8).
uppercase boolean no Return uppercase hex digests.
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/hash-generator \
  -H "Content-Type: application/json" \
  -d '{"text":"hello"}'

Example response

{
    "data": {
        "md5": "5d41402abc4b2a76b9719d911017c592",
        "sha1": "aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d",
        "sha256": "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824",
        "sha384": "59e1748777448c69de6b800d7a33bbfb9ff1b463e44354c3553bcdb9c666fa90125a3c79f90397bdf5f6a13de828684f",
        "sha512": "9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043"
    },
    "meta": {
        "tool": "hash-generator"
    }
}

UUID Generator

Generate random UUID v4 or time-ordered UUID v7 identifiers online, in bulk up to 500 at once. Uppercase and no-hyphen options. Free, also via API.

POST https://synsi.nl/api/v1/tools/uuid-generator

Parameters

Parameter Type Required Description
version string no v4 = random, v7 = time-ordered (sortable).
v4 · v7
default: v4
count integer no
default: 1
uppercase boolean no
default: false
hyphens boolean no
default: true

Example request

curl -X POST https://synsi.nl/api/v1/tools/uuid-generator \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "uuids": [
            "f1f43cc2-a248-4122-8e22-2841ea7d2451"
        ]
    },
    "meta": {
        "tool": "uuid-generator"
    }
}

SSL Certificate Checker

Free SSL certificate checker: see a domain's chain, expiry, SANs, issuer and trust, or decode a PEM certificate – PKIoverheid and UZI too.

POST https://synsi.nl/api/v1/tools/certificate-viewer

Parameters

Parameter Type Required Description
mode string no host: fetch the certificate chain from a TLS server; pem: decode pasted certificates.
host · pem
default: host
host string no Host name (optionally with :port, e.g. mail.example.com:993) for mode=host.
pem string no One or more PEM certificates (or base64 DER) for mode=pem.

Example request

curl -X POST https://synsi.nl/api/v1/tools/certificate-viewer \
  -H "Content-Type: application/json" \
  -d '{"host":"synsi.nl"}'

Password Generator

Generate strong, random passwords with letters, numbers and symbols. Choose the length, exclude look-alike characters and see the entropy. Free and private.

POST https://synsi.nl/api/v1/tools/password-generator

Parameters

Parameter Type Required Description
length integer no
default: 16
lowercase boolean no
default: true
uppercase boolean no
default: true
numbers boolean no
default: true
symbols boolean no
default: true
exclude_ambiguous boolean no Exclude look-alike characters (I, l, 1, O, 0, o).
default: false
count integer no
default: 1

Example request

curl -X POST https://synsi.nl/api/v1/tools/password-generator \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "passwords": [
            "V7C7=mK5Vy-Y[60D"
        ],
        "entropy_bits": 103.6
    },
    "meta": {
        "tool": "password-generator"
    }
}

Percentage Calculator

Free percentage calculator: find X% of Y, what percent X is of Y, the percentage change between two numbers, or add and subtract a percentage.

POST https://synsi.nl/api/v1/tools/percentage-calculator

Parameters

Parameter Type Required Description
mode string no percent_of: x% of y · what_percent: x is what % of y · change: % change from x to y · increase: y + x% · decrease: y - x%
percent_of · what_percent · change · increase · decrease
default: percent_of
x number yes
y number yes

Example request

curl -X POST https://synsi.nl/api/v1/tools/percentage-calculator \
  -H "Content-Type: application/json" \
  -d '{"x":15,"y":200}'

Example response

{
    "data": {
        "result": 30
    },
    "meta": {
        "tool": "percentage-calculator"
    }
}

VAT Calculator

Free VAT calculator: add VAT to a net price or remove VAT from a gross price. Up-to-date standard and reduced rates for EU countries, the UK and more.

POST https://synsi.nl/api/v1/tools/vat-calculator

Parameters

Parameter Type Required Description
amount number yes
rate number no VAT rate in percent.
default: 20
mode string no add: amount excludes VAT · remove: amount includes VAT
add · remove
default: add

Example request

curl -X POST https://synsi.nl/api/v1/tools/vat-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":100}'

Example response

{
    "data": {
        "net": 100,
        "vat": 20,
        "gross": 120,
        "rate": 20
    },
    "meta": {
        "tool": "vat-calculator"
    }
}

Age Calculator

Calculate your exact age in years, months and days, plus total weeks and days lived and the days until your next birthday. Free online age calculator.

POST https://synsi.nl/api/v1/tools/age-calculator

Parameters

Parameter Type Required Description
birth_date string (date) yes
on_date string (date) no Calculate the age on this date (default: today).

Example request

curl -X POST https://synsi.nl/api/v1/tools/age-calculator \
  -H "Content-Type: application/json" \
  -d '{"birth_date":"1990-05-17"}'

Example response

{
    "data": {
        "years": 36,
        "months": 5,
        "days": 8,
        "total_months": 437,
        "total_weeks": 1901,
        "total_days": 13310,
        "next_birthday_days": 204,
        "birth_weekday": 4
    },
    "meta": {
        "tool": "age-calculator"
    }
}

eID 4.4 SAML Validator

Validate DV or LC SAML metadata against eID SAML 4.4: XML schema, signature, PKIoverheid certificates, OIN, entityID, endpoints and algorithms. Free, nothing stored.

POST https://synsi.nl/api/v1/tools/eid-saml-validator

Parameters

Parameter Type Required Description
mode string no xml: validate the metadata in `xml`; url: fetch it from `url` first.
xml · url
default: xml
xml string no SAML metadata XML (an EntityDescriptor or EntitiesDescriptor) for mode=xml.
url string no https:// URL of the metadata for mode=url.

Example request

curl -X POST https://synsi.nl/api/v1/tools/eid-saml-validator \
  -H "Content-Type: application/json" \
  -d '{"url":"https://example.com/saml/metadata.xml"}'

Days Between Dates

Count the days between two dates, including weeks, months, years, hours and business days (Mon–Fri). Option to include the end date. Free calculator.

POST https://synsi.nl/api/v1/tools/date-difference

Parameters

Parameter Type Required Description
start_date string (date) yes
end_date string (date) yes
include_end boolean no Count the end date as a full day.
default: false

Example request

curl -X POST https://synsi.nl/api/v1/tools/date-difference \
  -H "Content-Type: application/json" \
  -d '{"start_date":"2026-01-01","end_date":"2026-12-31"}'

Example response

{
    "data": {
        "negative": false,
        "years": 0,
        "months": 11,
        "days": 30,
        "total_days": 364,
        "weeks": 52,
        "remaining_days": 0,
        "business_days": 260,
        "total_hours": 8736
    },
    "meta": {
        "tool": "date-difference"
    }
}

BMI Calculator

Calculate your body mass index (BMI) in metric or imperial units, see your WHO weight category and the healthy weight range for your height. Free.

POST https://synsi.nl/api/v1/tools/bmi-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
weight number yes
height number yes Height in cm (metric) or inches (imperial).

Example request

curl -X POST https://synsi.nl/api/v1/tools/bmi-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":175}'

Example response

{
    "data": {
        "bmi": 22.9,
        "category": "normal",
        "healthy_weight_min": 56.7,
        "healthy_weight_max": 76.3
    },
    "meta": {
        "tool": "bmi-calculator"
    }
}

Fraction Calculator

Add, subtract, multiply, divide or simplify fractions and see the exact result and decimal equivalent.

POST https://synsi.nl/api/v1/tools/fraction-calculator

Parameters

Parameter Type Required Description
numerator_a integer no
default: 1
denominator_a integer no
default: 2
numerator_b integer no
default: 1
denominator_b integer no
default: 3
mode string no
simplify · add · subtract · multiply · divide
default: simplify

Example request

curl -X POST https://synsi.nl/api/v1/tools/fraction-calculator \
  -H "Content-Type: application/json" \
  -d '{"numerator_a":1,"denominator_a":2,"numerator_b":1,"denominator_b":3}'

Example response

{
    "data": {
        "numerator": 1,
        "denominator": 2,
        "decimal": 0.5
    },
    "meta": {
        "tool": "fraction-calculator"
    }
}

Unit Converter

Free unit converter for 20+ categories including length, weight, temperature, volume, data storage, internet speed, pressure, energy, power, fuel economy and electrical units.

POST https://synsi.nl/api/v1/tools/unit-converter

Parameters

Parameter Type Required Description
category string no
length · weight · volume · area · speed · time · data · data-rate · temperature · cooking · pressure · energy · power · frequency · angle · force · torque · fuel-economy · density · acceleration · illuminance · voltage · current · resistance
default: length
value number yes
from string yes
mm · cm · dm · m · km · in · ft · yd · mi · nmi · mg · g · kg · t · oz · lb · st · ml · cl · dl · l · m3 · tsp · tbsp · floz · cup · pt · qt · gal · ukgal · mm2 · cm2 · m2 · ha · km2 · in2 · ft2 · yd2 · ac · mi2 · m/s · km/h · mph · kn · ft/s · ms · s · min · h · d · wk · yr · bit · Kbit · Mbit · Gbit · B · KB · MB · GB · TB · PB · KiB · MiB · GiB · TiB · bit/s · Kbit/s · Mbit/s · Gbit/s · B/s · KB/s · MB/s · GB/s · KiB/s · MiB/s · GiB/s · C · F · K · Pa · kPa · MPa · bar · mbar · psi · atm · torr · J · kJ · MJ · Wh · kWh · cal · kcal · BTU · W · kW · MW · hp · metric-hp · BTU/h · Hz · kHz · MHz · GHz · THz · rpm · rad · deg · arcmin · arcsec · grad · N · kN · dyn · kgf · lbf · Nm · kNm · lb-ft · lb-in · km/L · L/100km · mpg-us · mpg-uk · kg/m3 · g/cm3 · g/ml · lb/ft3 · lb/gal-us · m/s2 · g0 · ft/s2 · lx · klx · fc · phot · V · mV · kV · A · mA · kA · ohm · kohm · Mohm · mohm
to string yes
mm · cm · dm · m · km · in · ft · yd · mi · nmi · mg · g · kg · t · oz · lb · st · ml · cl · dl · l · m3 · tsp · tbsp · floz · cup · pt · qt · gal · ukgal · mm2 · cm2 · m2 · ha · km2 · in2 · ft2 · yd2 · ac · mi2 · m/s · km/h · mph · kn · ft/s · ms · s · min · h · d · wk · yr · bit · Kbit · Mbit · Gbit · B · KB · MB · GB · TB · PB · KiB · MiB · GiB · TiB · bit/s · Kbit/s · Mbit/s · Gbit/s · B/s · KB/s · MB/s · GB/s · KiB/s · MiB/s · GiB/s · C · F · K · Pa · kPa · MPa · bar · mbar · psi · atm · torr · J · kJ · MJ · Wh · kWh · cal · kcal · BTU · W · kW · MW · hp · metric-hp · BTU/h · Hz · kHz · MHz · GHz · THz · rpm · rad · deg · arcmin · arcsec · grad · N · kN · dyn · kgf · lbf · Nm · kNm · lb-ft · lb-in · km/L · L/100km · mpg-us · mpg-uk · kg/m3 · g/cm3 · g/ml · lb/ft3 · lb/gal-us · m/s2 · g0 · ft/s2 · lx · klx · fc · phot · V · mV · kV · A · mA · kA · ohm · kohm · Mohm · mohm
ingredient string no
flour · sugar · brown-sugar · butter · honey · rice · water · cocoa · oats
default: water

Example request

curl -X POST https://synsi.nl/api/v1/tools/unit-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"cm","to":"in"}'

Example response

{
    "data": {
        "result": 3.93700787402
    },
    "meta": {
        "tool": "unit-converter"
    }
}

Ratio Calculator

Simplify a two-part ratio and calculate each part as a percentage of the total.

POST https://synsi.nl/api/v1/tools/ratio-calculator

Parameters

Parameter Type Required Description
a number no
default: 3
b number no
default: 4

Example request

curl -X POST https://synsi.nl/api/v1/tools/ratio-calculator \
  -H "Content-Type: application/json" \
  -d '{"a":3,"b":4}'

Example response

{
    "data": {
        "ratio": "3:4",
        "part_a": 42.85714286,
        "part_b": 57.14285714
    },
    "meta": {
        "tool": "ratio-calculator"
    }
}

Animal Age Calculator

Convert your pet’s age to human years: dogs (by size), cats, rabbits, guinea pigs, hamsters and horses. Free animal age calculator with age charts.

POST https://synsi.nl/api/v1/tools/pet-age-calculator

Parameters

Parameter Type Required Description
animal string no
dog · cat · rabbit · guinea_pig · hamster · horse
default: dog
age number yes Age of the animal in years (decimals allowed, e.g. 0.5 for six months).
size string no Dogs only: small < 9 kg, medium 9–23 kg, large 23–41 kg, giant > 41 kg.
small · medium · large · giant
default: medium
method string no Dogs only: size chart, or the epigenetic formula 16 × ln(age) + 31.
chart · epigenetic
default: chart

Example request

curl -X POST https://synsi.nl/api/v1/tools/pet-age-calculator \
  -H "Content-Type: application/json" \
  -d '{"age":3}'

Example response

{
    "data": {
        "human_years": 28,
        "stage": "adult",
        "method": "chart"
    },
    "meta": {
        "tool": "pet-age-calculator"
    }
}

Average Calculator

Find the arithmetic mean of a list of numbers, together with their sum and count.

POST https://synsi.nl/api/v1/tools/average-calculator

Parameters

Parameter Type Required Description
numbers string yes
default: 1, 2, 3, 4, 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/average-calculator \
  -H "Content-Type: application/json" \
  -d '{"numbers":"1, 2, 3, 4, 5"}'

Example response

{
    "data": {
        "average": 3,
        "count": 5,
        "sum": 15
    },
    "meta": {
        "tool": "average-calculator"
    }
}

Interest Calculator

Free interest calculator: see how your savings grow with compound or simple interest, monthly deposits and a year-by-year overview. No sign-up.

POST https://synsi.nl/api/v1/tools/interest-calculator

Parameters

Parameter Type Required Description
principal number yes Starting amount.
rate number yes Annual interest rate in percent.
years integer yes
monthly_deposit number no Amount added at the end of every month.
default: 0
compounding string no How often interest is added; "simple" pays interest on deposits only, never on interest.
yearly · quarterly · monthly · daily · simple
default: monthly

Example request

curl -X POST https://synsi.nl/api/v1/tools/interest-calculator \
  -H "Content-Type: application/json" \
  -d '{"principal":10000,"rate":4,"years":10}'

Example response

{
    "data": {
        "final_balance": 14908.33,
        "total_contributed": 10000,
        "total_interest": 4908.33,
        "effective_rate": 4.0742,
        "schedule": [
            {
                "year": 1,
                "balance": 10407.42,
                "contributed": 10000,
                "interest": 407.42
            },
            {
                "year": 2,
                "balance": 10831.43,
                "contributed": 10000,
                "interest": 831.43
            },
            {
                "year": 3,
                "balance": 11272.72,
                "contributed": 10000,
                "interest": 1272.72
            },
            {
                "year": 4,
                "balance": 11731.99,
                "contributed": 10000,
                "interest": 1731.99
            },
            {
                "year": 5,
                "balance": 12209.97,
                "contributed": 10000,
                "interest": 2209.97
            },
            {
                "year": 6,
                "balance": 12707.42,
                "contributed": 10000,
                "interest": 2707.42
            },
            {
                "year": 7,
                "balance": 13225.14,
                "contributed": 10000,
                "interest": 3225.14
            },
            {
                "year": 8,
                "balance": 13763.95,
                "contributed": 10000,
                "interest": 3763.95
            },
            {
                "year": 9,
                "balance": 14324.72,
                "contributed": 10000,
                "interest": 4324.72
            },
            {
                "year": 10,
                "balance": 14908.33,
                "contributed": 10000,
                "interest": 4908.33
            }
        ]
    },
    "meta": {
        "tool": "interest-calculator"
    }
}

Week Number Calculator

Find the ISO 8601 week number for any date. See the week-year, weekday, and Monday-to-Sunday dates with this free week calculator.

POST https://synsi.nl/api/v1/tools/week-number

Parameters

Parameter Type Required Description
date string (date) no Date for which to find the ISO 8601 week number.

Example request

curl -X POST https://synsi.nl/api/v1/tools/week-number \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "week_number": 43,
        "week_year": 2026,
        "weekday": 7,
        "week_start": "2026-10-19",
        "week_end": "2026-10-25"
    },
    "meta": {
        "tool": "week-number"
    }
}

Probability Calculator

Calculate the probability of an event from favorable outcomes and the total number of equally likely outcomes.

POST https://synsi.nl/api/v1/tools/probability-calculator

Parameters

Parameter Type Required Description
favorable number no
default: 1
total number no
default: 6

Example request

curl -X POST https://synsi.nl/api/v1/tools/probability-calculator \
  -H "Content-Type: application/json" \
  -d '{"favorable":1,"total":6}'

Example response

{
    "data": {
        "probability": 0.16666667,
        "percent": 16.66666667,
        "odds": "1:5"
    },
    "meta": {
        "tool": "probability-calculator"
    }
}

eTD Service Catalogue Editor

Load an OIN's entries from the eTD service catalogue, edit service definitions, instances, attributes, classifiers and certificates, and generate checked catalogue XML. Free.

POST https://synsi.nl/api/v1/tools/etd-service-catalog

Parameters

Parameter Type Required Description
mode string no load: the catalogue entries of `oin` from the aggregator, as XML and as the editor model; import: read pasted catalogue XML (`xml`) into the editor model; validate: check catalogue XML (`xml`) against the Afsprakenstelsel 1.13.
load · import · validate
default: load
oin string no 20-digit OIN of the service provider, for mode=load.
environment string no Which aggregator catalogue to load from, for mode=load.
production · test
default: production
xml string no Service catalogue XML (a ServiceCatalogue or ServiceProvider element), for mode=import and mode=validate.

Example request

curl -X POST https://synsi.nl/api/v1/tools/etd-service-catalog \
  -H "Content-Type: application/json" \
  -d '{"oin":"00000001003214394000"}'

Loan Calculator

Free loan calculator: work out the monthly payment, total interest and year-by-year amortization of an annuity or linear loan. No sign-up.

POST https://synsi.nl/api/v1/tools/loan-calculator

Parameters

Parameter Type Required Description
amount number yes Loan amount.
rate number yes Annual interest rate in percent.
years integer yes Term in years.
type string no annuity: equal monthly payments · linear: equal monthly repayments, decreasing interest
annuity · linear
default: annuity

Example request

curl -X POST https://synsi.nl/api/v1/tools/loan-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":25000,"rate":6,"years":5}'

Example response

{
    "data": {
        "first_payment": 483.32,
        "last_payment": 483.32,
        "total_paid": 28999.2,
        "total_interest": 3999.2,
        "schedule": [
            {
                "year": 1,
                "principal": 4420.08,
                "interest": 1379.76,
                "balance": 20579.92
            },
            {
                "year": 2,
                "principal": 4692.7,
                "interest": 1107.14,
                "balance": 15887.22
            },
            {
                "year": 3,
                "principal": 4982.14,
                "interest": 817.7,
                "balance": 10905.09
            },
            {
                "year": 4,
                "principal": 5289.42,
                "interest": 510.42,
                "balance": 5615.66
            },
            {
                "year": 5,
                "principal": 5615.66,
                "interest": 184.18,
                "balance": 0
            }
        ]
    },
    "meta": {
        "tool": "loan-calculator"
    }
}

Baby Boy Name Generator

Generate baby boy name ideas and filter them by first letter. Explore timeless and modern names, then copy or download your shortlist for free.

POST https://synsi.nl/api/v1/tools/baby-boy-name-generator

Parameters

Parameter Type Required Description
count integer no Number of names to generate.
default: 10
first_letter string no Optionally choose a first letter.
any · a · b · c · d · e · f · g · h · i · j · k · l · m · n · o · p · q · r · s · t · u · v · w · x · y · z
default: any

Example request

curl -X POST https://synsi.nl/api/v1/tools/baby-boy-name-generator \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "names": [
            "Hugo",
            "Bennett",
            "Declan",
            "Rafael",
            "Jack",
            "Mason",
            "Isaac",
            "Malachi",
            "Jude",
            "Levi"
        ],
        "count": 10
    },
    "meta": {
        "tool": "baby-boy-name-generator"
    }
}

Standard Deviation Calculator

Calculate the mean, variance and standard deviation of a data set using a population or sample formula.

POST https://synsi.nl/api/v1/tools/standard-deviation-calculator

Parameters

Parameter Type Required Description
numbers string yes
default: 1, 2, 3, 4, 5
mode string no
population · sample
default: population

Example request

curl -X POST https://synsi.nl/api/v1/tools/standard-deviation-calculator \
  -H "Content-Type: application/json" \
  -d '{"numbers":"1, 2, 3, 4, 5"}'

Example response

{
    "data": {
        "mean": 3,
        "variance": 2,
        "standard_deviation": 1.41421356,
        "count": 5
    },
    "meta": {
        "tool": "standard-deviation-calculator"
    }
}

Inflation Calculator

Free inflation calculator: see what something will cost in the future or how much your money will be worth, at any yearly inflation rate.

POST https://synsi.nl/api/v1/tools/inflation-calculator

Parameters

Parameter Type Required Description
amount number yes
rate number no Average yearly inflation in percent.
default: 2
years integer yes
mode string no future_cost: what something costs after N years · purchasing_power: what the amount is worth after N years
future_cost · purchasing_power
default: future_cost

Example request

curl -X POST https://synsi.nl/api/v1/tools/inflation-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":1000,"years":10}'

Example response

{
    "data": {
        "result": 1218.99,
        "difference": 218.99,
        "change_percent": 21.9,
        "cumulative_inflation": 21.9,
        "schedule": [
            {
                "year": 1,
                "value": 1020
            },
            {
                "year": 2,
                "value": 1040.4
            },
            {
                "year": 3,
                "value": 1061.21
            },
            {
                "year": 4,
                "value": 1082.43
            },
            {
                "year": 5,
                "value": 1104.08
            },
            {
                "year": 6,
                "value": 1126.16
            },
            {
                "year": 7,
                "value": 1148.69
            },
            {
                "year": 8,
                "value": 1171.66
            },
            {
                "year": 9,
                "value": 1195.09
            },
            {
                "year": 10,
                "value": 1218.99
            }
        ]
    },
    "meta": {
        "tool": "inflation-calculator"
    }
}

Baby Girl Name Generator

Generate baby girl name ideas and filter them by first letter. Explore timeless and modern names, then copy or download your shortlist for free.

POST https://synsi.nl/api/v1/tools/baby-girl-name-generator

Parameters

Parameter Type Required Description
count integer no Number of names to generate.
default: 10
first_letter string no Optionally choose a first letter.
any · a · b · c · d · e · f · g · h · i · j · k · l · m · n · o · p · q · r · s · t · u · v · w · x · y · z
default: any

Example request

curl -X POST https://synsi.nl/api/v1/tools/baby-girl-name-generator \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "names": [
            "Hannah",
            "Emily",
            "Margaret",
            "Anna",
            "Beatrice",
            "Maeve",
            "Imogen",
            "Natalia",
            "Lucia",
            "Violet"
        ],
        "count": 10
    },
    "meta": {
        "tool": "baby-girl-name-generator"
    }
}

Variance Calculator

Calculate population or sample variance and standard deviation from a list of observations.

POST https://synsi.nl/api/v1/tools/variance-calculator

Parameters

Parameter Type Required Description
numbers string yes
default: 1, 2, 3, 4, 5
mode string no
population · sample
default: population

Example request

curl -X POST https://synsi.nl/api/v1/tools/variance-calculator \
  -H "Content-Type: application/json" \
  -d '{"numbers":"1, 2, 3, 4, 5"}'

Example response

{
    "data": {
        "mean": 3,
        "variance": 2,
        "standard_deviation": 1.41421356,
        "count": 5
    },
    "meta": {
        "tool": "variance-calculator"
    }
}

Image Converter

Free image converter: convert JPG, PNG, WebP, GIF and AVIF to JPG, PNG or WebP and resize them – in your browser, without uploading. Batch + ZIP.

POST https://synsi.nl/api/v1/tools/image-converter

Parameters

Parameter Type Required Description
image string (binary) yes The image to convert.
format string no Output format.
jpg · png · webp
default: webp
quality integer no Quality for JPG and WebP (1–100).
default: 85
max_width integer no Optional: scale down to at most this width (keeps the aspect ratio).
max_height integer no Optional: scale down to at most this height (keeps the aspect ratio).

Example request

curl -X POST https://synsi.nl/api/v1/tools/image-converter \
  -F "image=@photo.png" \
  -F "format=webp" \
  -F "quality=80" \
  -o result

File tools take multipart/form-data and return the converted file directly (Content-Type and Content-Disposition headers are set).

Body Fat Calculator

Estimate body fat percentage from age, height, weight and sex with a BMI-based equation. Includes metric and imperial units. Free adult calculator.

POST https://synsi.nl/api/v1/tools/body-fat-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
sex string no Sex coefficient used by the Deurenberg equation.
female · male
default: female
age integer no Age in years.
default: 30
weight number no Weight in kg or lb according to unit.
default: 70
height number no Height in cm or inches according to unit.
default: 165

Example request

curl -X POST https://synsi.nl/api/v1/tools/body-fat-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":165}'

Example response

{
    "data": {
        "body_fat_percentage": 32.4,
        "bmi": 25.7
    },
    "meta": {
        "tool": "body-fat-calculator"
    }
}

Percentage Change Calculator

Calculate the percentage increase or decrease between an original value and a new value.

POST https://synsi.nl/api/v1/tools/percentage-change-calculator

Parameters

Parameter Type Required Description
from_value number no
default: 100
to_value number no
default: 125

Example request

curl -X POST https://synsi.nl/api/v1/tools/percentage-change-calculator \
  -H "Content-Type: application/json" \
  -d '{"from_value":100,"to_value":125}'

Example response

{
    "data": {
        "change_percent": 25,
        "difference": 25
    },
    "meta": {
        "tool": "percentage-change-calculator"
    }
}

TDEE Calculator

Estimate your total daily energy expenditure (TDEE) from age, height, weight and activity level. Includes metric and imperial units. Free adult calorie calculator.

POST https://synsi.nl/api/v1/tools/tdee-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
sex string no Sex coefficient used by the Mifflin–St Jeor equation.
female · male
default: female
age integer no Age in years.
default: 30
weight number no Weight in kg or lb according to unit.
default: 70
height number no Height in cm or inches according to unit.
default: 165
activity string no Activity multiplier for estimated daily energy use.
sedentary · light · moderate · active · very_active
default: moderate

Example request

curl -X POST https://synsi.nl/api/v1/tools/tdee-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":165}'

Example response

{
    "data": {
        "bmr": 1420,
        "tdee": 2201,
        "activity": "moderate"
    },
    "meta": {
        "tool": "tdee-calculator"
    }
}

BMR Calculator

Estimate your basal metabolic rate (BMR) from age, height, weight and sex. Supports metric and imperial units. Free adult BMR calculator.

POST https://synsi.nl/api/v1/tools/bmr-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
sex string no Sex coefficient used by the Mifflin–St Jeor equation.
female · male
default: female
age integer no Age in years.
default: 30
weight number no Weight in kg or lb according to unit.
default: 70
height number no Height in cm or inches according to unit.
default: 165

Example request

curl -X POST https://synsi.nl/api/v1/tools/bmr-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":165}'

Example response

{
    "data": {
        "bmr": 1420
    },
    "meta": {
        "tool": "bmr-calculator"
    }
}

GCD and LCM Calculator

Find the greatest common divisor (GCD) and least common multiple (LCM) of two whole numbers.

POST https://synsi.nl/api/v1/tools/gcd-lcm-calculator

Parameters

Parameter Type Required Description
a integer no
default: 24
b integer no
default: 36

Example request

curl -X POST https://synsi.nl/api/v1/tools/gcd-lcm-calculator \
  -H "Content-Type: application/json" \
  -d '{"a":24,"b":36}'

Example response

{
    "data": {
        "gcd": 12,
        "lcm": 72
    },
    "meta": {
        "tool": "gcd-lcm-calculator"
    }
}

Calorie Calculator

Estimate how many calories you need each day to maintain your weight. Enter your age, height, weight and activity level. Free calculator for adults.

POST https://synsi.nl/api/v1/tools/calorie-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
sex string no Sex coefficient used by the Mifflin–St Jeor equation.
female · male
default: female
age integer no Age in years.
default: 30
weight number no Weight in kg or lb according to unit.
default: 70
height number no Height in cm or inches according to unit.
default: 165
activity string no Activity multiplier for estimated daily energy use.
sedentary · light · moderate · active · very_active
default: moderate

Example request

curl -X POST https://synsi.nl/api/v1/tools/calorie-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":165}'

Example response

{
    "data": {
        "calories": 2201,
        "bmr": 1420,
        "activity": "moderate"
    },
    "meta": {
        "tool": "calorie-calculator"
    }
}

Scientific Calculator

Evaluate common scientific functions including trigonometry, logarithms, powers, roots and reciprocals.

POST https://synsi.nl/api/v1/tools/scientific-calculator

Parameters

Parameter Type Required Description
value number no
default: 30
mode string no
sin · cos · tan · asin · acos · atan · ln · log10 · sqrt · square · cube · exp · reciprocal · abs
default: sin
angle_unit string no
degrees · radians
default: degrees

Example request

curl -X POST https://synsi.nl/api/v1/tools/scientific-calculator \
  -H "Content-Type: application/json" \
  -d '{"value":30}'

Example response

{
    "data": {
        "result": 0.5
    },
    "meta": {
        "tool": "scientific-calculator"
    }
}

Quadratic Equation Calculator

Solve a quadratic equation in the form ax² + bx + c = 0 and inspect its discriminant and roots.

POST https://synsi.nl/api/v1/tools/quadratic-equation-calculator

Parameters

Parameter Type Required Description
a number no
default: 1
b number no
default: -3
c number no
default: 2

Example request

curl -X POST https://synsi.nl/api/v1/tools/quadratic-equation-calculator \
  -H "Content-Type: application/json" \
  -d '{"a":1,"b":-3,"c":2}'

Example response

{
    "data": {
        "discriminant": 1,
        "root_1": 1,
        "root_2": 2
    },
    "meta": {
        "tool": "quadratic-equation-calculator"
    }
}

Ideal Weight Calculator

Estimate an adult weight range for your height based on BMI values of 18.5 to 24.9. Includes metric and imperial units and a reference midpoint.

POST https://synsi.nl/api/v1/tools/ideal-weight-calculator

Parameters

Parameter Type Required Description
unit string no metric: cm · imperial: inches
metric · imperial
default: metric
height number no Height in cm or inches according to unit.
default: 170

Example request

curl -X POST https://synsi.nl/api/v1/tools/ideal-weight-calculator \
  -H "Content-Type: application/json" \
  -d '{"height":170}'

Example response

{
    "data": {
        "weight_min": 53.5,
        "weight_midpoint": 62.7,
        "weight_max": 72
    },
    "meta": {
        "tool": "ideal-weight-calculator"
    }
}

Calorie Deficit Calculator

Estimate maintenance calories and a goal-based daily target from your age, height, weight and activity. Compare BMR formulas and see optional macro estimates.

POST https://synsi.nl/api/v1/tools/calorie-deficit-calculator

Parameters

Parameter Type Required Description
unit string no metric: kg + cm · imperial: lb + inches
metric · imperial
default: metric
sex string no Sex coefficient used by the Mifflin–St Jeor equation.
female · male
default: female
age integer no Age in years.
default: 30
weight number no Weight in kg or lb according to unit.
default: 70
height number no Height in cm or inches according to unit.
default: 165
activity string no Activity multiplier for estimated daily energy use.
sedentary · light · moderate · active · very_active
default: moderate
goal string no Adjustment to estimated maintenance calories.
lose_mild · lose_moderate · maintain · gain_mild · gain_moderate
default: lose_mild
formula string no BMR estimation formula. Katch–McArdle uses body-fat percentage.
mifflin · katch
default: mifflin
body_fat_percentage number no Estimated body-fat percentage, used by Katch–McArdle.
default: 25
macro_profile string no Macro calorie split used to estimate grams per day.
balanced · higher_protein · lower_carb
default: balanced

Example request

curl -X POST https://synsi.nl/api/v1/tools/calorie-deficit-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"height":165}'

Example response

{
    "data": {
        "bmr": 1420,
        "maintenance_calories": 2201,
        "target_calories": 1981,
        "daily_difference": 220,
        "weekly_difference": 1540,
        "direction": "deficit",
        "macros": {
            "carbohydrates_g": 248,
            "protein_g": 99,
            "fat_g": 66
        },
        "macro_profile": "balanced"
    },
    "meta": {
        "tool": "calorie-deficit-calculator"
    }
}

Linear Equation Calculator

Solve a linear equation in the form ax + b = 0 for x.

POST https://synsi.nl/api/v1/tools/linear-equation-calculator

Parameters

Parameter Type Required Description
a number no
default: 2
b number no
default: -8

Example request

curl -X POST https://synsi.nl/api/v1/tools/linear-equation-calculator \
  -H "Content-Type: application/json" \
  -d '{"a":2,"b":-8}'

Example response

{
    "data": {
        "solution": 4
    },
    "meta": {
        "tool": "linear-equation-calculator"
    }
}

Exponent Calculator

Calculate a base raised to a power, including fractional and negative exponents.

POST https://synsi.nl/api/v1/tools/exponent-calculator

Parameters

Parameter Type Required Description
base number no
default: 2
exponent number no
default: 8

Example request

curl -X POST https://synsi.nl/api/v1/tools/exponent-calculator \
  -H "Content-Type: application/json" \
  -d '{"base":2,"exponent":8}'

Example response

{
    "data": {
        "result": 256
    },
    "meta": {
        "tool": "exponent-calculator"
    }
}

Logarithm Calculator

Calculate a logarithm for any positive value and valid positive base other than one.

POST https://synsi.nl/api/v1/tools/logarithm-calculator

Parameters

Parameter Type Required Description
value number no
default: 100
base number no
default: 10

Example request

curl -X POST https://synsi.nl/api/v1/tools/logarithm-calculator \
  -H "Content-Type: application/json" \
  -d '{"value":100,"base":10}'

Example response

{
    "data": {
        "result": 2
    },
    "meta": {
        "tool": "logarithm-calculator"
    }
}

Square Root Calculator

Find the principal square root of a non-negative number.

POST https://synsi.nl/api/v1/tools/square-root-calculator

Parameters

Parameter Type Required Description
value number no
default: 144

Example request

curl -X POST https://synsi.nl/api/v1/tools/square-root-calculator \
  -H "Content-Type: application/json" \
  -d '{"value":144}'

Example response

{
    "data": {
        "result": 12
    },
    "meta": {
        "tool": "square-root-calculator"
    }
}

File to PDF Converter

Convert Word, Excel, TXT, JSON, Markdown, CSV, XML, HTML and images to PDF online. Free file to PDF converter, up to 20 MB.

POST https://synsi.nl/api/v1/tools/file-to-pdf

Parameters

Parameter Type Required Description
file string (binary) yes JPG, PNG, WebP, GIF, BMP, TXT, JSON, Markdown, CSV, XML, HTML, RTF, DOCX or XLSX; max 20 MB.

Example request

curl -X POST https://synsi.nl/api/v1/tools/file-to-pdf \
  -F "image=@photo.png" \
  -o result

File tools take multipart/form-data and return the converted file directly (Content-Type and Content-Disposition headers are set).

Factorial Calculator

Calculate n factorial, the product of all positive integers up to n.

POST https://synsi.nl/api/v1/tools/factorial-calculator

Parameters

Parameter Type Required Description
n integer no
default: 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/factorial-calculator \
  -H "Content-Type: application/json" \
  -d '{"n":5}'

Example response

{
    "data": {
        "result": 120
    },
    "meta": {
        "tool": "factorial-calculator"
    }
}

Permutation and Combination Calculator

Calculate arrangements where order matters (permutations) or selections where it does not (combinations).

POST https://synsi.nl/api/v1/tools/permutation-combination-calculator

Parameters

Parameter Type Required Description
n integer no
default: 10
r integer no
default: 3
mode string no
permutation · combination
default: combination

Example request

curl -X POST https://synsi.nl/api/v1/tools/permutation-combination-calculator \
  -H "Content-Type: application/json" \
  -d '{"n":10,"r":3}'

Example response

{
    "data": {
        "result": 120
    },
    "meta": {
        "tool": "permutation-combination-calculator"
    }
}

Z-Score Calculator

Convert a value to a z-score using its mean and standard deviation.

POST https://synsi.nl/api/v1/tools/z-score-calculator

Parameters

Parameter Type Required Description
x number no
default: 85
mean number no
default: 70
standard_deviation number no
default: 10

Example request

curl -X POST https://synsi.nl/api/v1/tools/z-score-calculator \
  -H "Content-Type: application/json" \
  -d '{"x":85,"mean":70,"standard_deviation":10}'

Example response

{
    "data": {
        "z_score": 1.5
    },
    "meta": {
        "tool": "z-score-calculator"
    }
}

Confidence Interval Calculator

Estimate a confidence interval for a mean using a sample mean, standard deviation, sample size and confidence level.

POST https://synsi.nl/api/v1/tools/confidence-interval-calculator

Parameters

Parameter Type Required Description
mean number no
default: 50
standard_deviation number no
default: 10
sample_size integer no
default: 100
confidence_level string no
90 · 95 · 99
default: 95

Example request

curl -X POST https://synsi.nl/api/v1/tools/confidence-interval-calculator \
  -H "Content-Type: application/json" \
  -d '{"mean":50,"standard_deviation":10,"sample_size":100}'

Example response

{
    "data": {
        "lower": 48.04003602,
        "upper": 51.95996398,
        "margin_of_error": 1.95996398
    },
    "meta": {
        "tool": "confidence-interval-calculator"
    }
}

Mean, Median and Mode Calculator

Calculate the mean, median, mode and count for a set of numbers.

POST https://synsi.nl/api/v1/tools/mean-median-mode-calculator

Parameters

Parameter Type Required Description
numbers string yes
default: 1, 2, 3, 4, 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/mean-median-mode-calculator \
  -H "Content-Type: application/json" \
  -d '{"numbers":"1, 2, 3, 4, 5"}'

Example response

{
    "data": {
        "mean": 3,
        "median": 3,
        "mode": "No mode",
        "count": 5
    },
    "meta": {
        "tool": "mean-median-mode-calculator"
    }
}

Range Calculator

Find the minimum, maximum and range of a list of numerical values.

POST https://synsi.nl/api/v1/tools/range-calculator

Parameters

Parameter Type Required Description
numbers string yes
default: 1, 2, 3, 4, 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/range-calculator \
  -H "Content-Type: application/json" \
  -d '{"numbers":"1, 2, 3, 4, 5"}'

Example response

{
    "data": {
        "minimum": 1,
        "maximum": 5,
        "range": 4
    },
    "meta": {
        "tool": "range-calculator"
    }
}

Linear Regression Calculator

Fit a straight line to paired x and y observations and calculate slope, intercept and R-squared.

POST https://synsi.nl/api/v1/tools/linear-regression-calculator

Parameters

Parameter Type Required Description
x_values string yes
default: 1, 2, 3, 4, 5
y_values string yes
default: 2, 4, 5, 4, 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/linear-regression-calculator \
  -H "Content-Type: application/json" \
  -d '{"x_values":"1, 2, 3, 4, 5","y_values":"2, 4, 5, 4, 5"}'

Example response

{
    "data": {
        "slope": 0.6,
        "intercept": 2.2,
        "r_squared": 0.6
    },
    "meta": {
        "tool": "linear-regression-calculator"
    }
}

Correlation Coefficient Calculator

Calculate Pearson’s correlation coefficient from paired x and y data.

POST https://synsi.nl/api/v1/tools/correlation-coefficient-calculator

Parameters

Parameter Type Required Description
x_values string yes
default: 1, 2, 3, 4, 5
y_values string yes
default: 2, 4, 5, 4, 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/correlation-coefficient-calculator \
  -H "Content-Type: application/json" \
  -d '{"x_values":"1, 2, 3, 4, 5","y_values":"2, 4, 5, 4, 5"}'

Example response

{
    "data": {
        "correlation": 0.77459667,
        "strength": "strong"
    },
    "meta": {
        "tool": "correlation-coefficient-calculator"
    }
}

P-Value Calculator

Estimate a one-tailed or two-tailed p-value from a z-score under the standard normal distribution.

POST https://synsi.nl/api/v1/tools/p-value-calculator

Parameters

Parameter Type Required Description
z_score number no
default: 1.96
mode string no
one · two
default: two

Example request

curl -X POST https://synsi.nl/api/v1/tools/p-value-calculator \
  -H "Content-Type: application/json" \
  -d '{"z_score":1.96}'

Example response

{
    "data": {
        "p_value": 0.04999579
    },
    "meta": {
        "tool": "p-value-calculator"
    }
}

Normal Distribution Calculator

Calculate the z-score, cumulative probability and probability density for a normal distribution.

POST https://synsi.nl/api/v1/tools/normal-distribution-calculator

Parameters

Parameter Type Required Description
x number no
default: 70
mean number no
default: 60
standard_deviation number no
default: 10

Example request

curl -X POST https://synsi.nl/api/v1/tools/normal-distribution-calculator \
  -H "Content-Type: application/json" \
  -d '{"x":70,"mean":60,"standard_deviation":10}'

Example response

{
    "data": {
        "z_score": 1,
        "cumulative_probability": 0.84134475,
        "density": 0.02419707
    },
    "meta": {
        "tool": "normal-distribution-calculator"
    }
}

Bayes' Theorem Calculator

Update a prior probability using a true-positive rate and false-positive rate to calculate a posterior probability.

POST https://synsi.nl/api/v1/tools/bayes-theorem-calculator

Parameters

Parameter Type Required Description
prior_probability number no
default: 1
true_positive_rate number no
default: 99
false_positive_rate number no
default: 5

Example request

curl -X POST https://synsi.nl/api/v1/tools/bayes-theorem-calculator \
  -H "Content-Type: application/json" \
  -d '{"prior_probability":1,"true_positive_rate":99,"false_positive_rate":5}'

Example response

{
    "data": {
        "posterior_probability": 0.16666667,
        "percent": 16.66666667
    },
    "meta": {
        "tool": "bayes-theorem-calculator"
    }
}

Date Add or Subtract Calculator

Add or subtract a number of days, weeks, months or years from a date, with month-end dates handled safely.

POST https://synsi.nl/api/v1/tools/date-add-subtract

Parameters

Parameter Type Required Description
date string (date) yes
amount integer no
default: 1
unit string no
days · weeks · months · years
default: days
operation string no
add · subtract
default: add

Example request

curl -X POST https://synsi.nl/api/v1/tools/date-add-subtract \
  -H "Content-Type: application/json" \
  -d '{"date":"2026-01-31","amount":1}'

Example response

{
    "data": {
        "result_date": "2026-02-01",
        "weekday": 7,
        "days_shifted": 1
    },
    "meta": {
        "tool": "date-add-subtract"
    }
}

Time Duration Calculator

Calculate the elapsed time between two clock times, including intervals that cross midnight.

POST https://synsi.nl/api/v1/tools/time-duration

Parameters

Parameter Type Required Description
start_time string yes
default: 09:00
end_time string yes
default: 17:00

Example request

curl -X POST https://synsi.nl/api/v1/tools/time-duration \
  -H "Content-Type: application/json" \
  -d '{"start_time":"09:00","end_time":"17:00"}'

Example response

{
    "data": {
        "duration": "08:00",
        "total_minutes": 480,
        "hours_decimal": 8
    },
    "meta": {
        "tool": "time-duration"
    }
}

Countdown Calculator

Count the days, full weeks and remaining days from a start date to a target date.

POST https://synsi.nl/api/v1/tools/countdown-calculator

Parameters

Parameter Type Required Description
from_date string (date) no
default: 2026-10-25
target_date string (date) no
default: 2026-11-24

Example request

curl -X POST https://synsi.nl/api/v1/tools/countdown-calculator \
  -H "Content-Type: application/json" \
  -d '{"from_date":"2026-01-01","target_date":"2026-01-31"}'

Example response

{
    "data": {
        "days_until": 30,
        "full_weeks": 4,
        "remaining_days": 2
    },
    "meta": {
        "tool": "countdown-calculator"
    }
}

Time Zone Converter

Convert a local date and time between common IANA time zones and see the UTC offset and Unix timestamp.

POST https://synsi.nl/api/v1/tools/timezone-converter

Parameters

Parameter Type Required Description
local_datetime string yes
default: 2026-10-25T00:39
from_timezone string no
UTC · Europe/Amsterdam · Europe/London · America/New_York · America/Los_Angeles · Asia/Dubai · Asia/Tokyo · Australia/Sydney
default: UTC
to_timezone string no
UTC · Europe/Amsterdam · Europe/London · America/New_York · America/Los_Angeles · Asia/Dubai · Asia/Tokyo · Australia/Sydney
default: Europe/Amsterdam

Example request

curl -X POST https://synsi.nl/api/v1/tools/timezone-converter \
  -H "Content-Type: application/json" \
  -d '{"local_datetime":"2026-01-15T12:00"}'

Example response

{
    "data": {
        "target_local": "2026-01-15T13:00",
        "target_offset": "+01:00",
        "unix_timestamp": 1768478400
    },
    "meta": {
        "tool": "timezone-converter"
    }
}

Unix Timestamp Converter

Convert Unix timestamps in seconds or milliseconds to a readable UTC date and back again.

POST https://synsi.nl/api/v1/tools/unix-timestamp-converter

Parameters

Parameter Type Required Description
timestamp integer no
default: 1767225600
unit string no
seconds · milliseconds
default: seconds

Example request

curl -X POST https://synsi.nl/api/v1/tools/unix-timestamp-converter \
  -H "Content-Type: application/json" \
  -d '{"timestamp":1767225600}'

Example response

{
    "data": {
        "utc_datetime": "2026-01-01T00:00:00.000Z",
        "unix_seconds": 1767225600,
        "unix_milliseconds": 1767225600000
    },
    "meta": {
        "tool": "unix-timestamp-converter"
    }
}

Leap Year Calculator

Check whether a year is a leap year and see how many days it contains.

POST https://synsi.nl/api/v1/tools/leap-year-calculator

Parameters

Parameter Type Required Description
year integer no
default: 2026

Example request

curl -X POST https://synsi.nl/api/v1/tools/leap-year-calculator \
  -H "Content-Type: application/json" \
  -d '{"year":2026}'

Example response

{
    "data": {
        "is_leap_year": false,
        "days_in_year": 365,
        "next_leap_year": 2028
    },
    "meta": {
        "tool": "leap-year-calculator"
    }
}

Calendar

Free online calendar: today’s date, ISO week number, day of the year and quarter, month and year views with week numbers, plus public holidays for 5 countries.

POST https://synsi.nl/api/v1/tools/calendar

Parameters

Parameter Type Required Description
date string (date) no The date (YYYY-MM-DD, from 1583). Defaults to today.
country string no Public holidays to include: Netherlands, Belgium, Germany (nationwide), United Kingdom (England & Wales) or United States (federal).
none · nl · be · de · gb · us
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/calendar \
  -H "Content-Type: application/json" \
  -d '{"country":"nl"}'

Example response

{
    "data": {
        "date": "2026-10-25",
        "weekday": 7,
        "day_of_year": 298,
        "days_in_year": 365,
        "days_remaining": 67,
        "iso_week": 43,
        "iso_week_year": 2026,
        "quarter": 4,
        "is_leap_year": false,
        "days_in_month": 31,
        "holidays_on_date": [],
        "holidays": [
            {
                "date": "2026-01-01",
                "key": "new_year",
                "name": "New Year's Day",
                "observed": false
            },
            {
                "date": "2026-04-03",
                "key": "good_friday",
                "name": "Good Friday",
                "observed": false
            },
            {
                "date": "2026-04-05",
                "key": "easter_sunday",
                "name": "Easter Sunday",
                "observed": false
            },
            {
                "date": "2026-04-06",
                "key": "easter_monday",
                "name": "Easter Monday",
                "observed": false
            },
            {
                "date": "2026-04-27",
                "key": "kings_day",
                "name": "King's Day",
                "observed": false
            },
            {
                "date": "2026-05-05",
                "key": "liberation_day",
                "name": "Liberation Day",
                "observed": false
            },
            {
                "date": "2026-05-14",
                "key": "ascension",
                "name": "Ascension Day",
                "observed": false
            },
            {
                "date": "2026-05-24",
                "key": "whit_sunday",
                "name": "Whit Sunday",
                "observed": false
            },
            {
                "date": "2026-05-25",
                "key": "whit_monday",
                "name": "Whit Monday",
                "observed": false
            },
            {
                "date": "2026-12-25",
                "key": "christmas",
                "name": "Christmas Day",
                "observed": false
            },
            {
                "date": "2026-12-26",
                "key": "second_christmas",
                "name": "Second Day of Christmas",
                "observed": false
            }
        ]
    },
    "meta": {
        "tool": "calendar"
    }
}

Protein Intake Calculator

Protein intake by body weight for general, active and athletic adults.

POST https://synsi.nl/api/v1/tools/protein-intake-calculator

Parameters

Parameter Type Required Description
weight number no weight
default: 70
unit string no unit
metric · imperial
default: metric
activity string no activity
general · active · athlete
default: active

Example request

curl -X POST https://synsi.nl/api/v1/tools/protein-intake-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70}'

Example response

{
    "data": {
        "min_g": 84,
        "max_g": 112,
        "weight_kg": 70
    },
    "meta": {
        "tool": "protein-intake-calculator"
    }
}

Water Intake Calculator

See a reference for total daily water intake based on life stage.

POST https://synsi.nl/api/v1/tools/water-intake-calculator

Parameters

Parameter Type Required Description
profile string no profile
woman · man · pregnancy · lactation
default: woman

Example request

curl -X POST https://synsi.nl/api/v1/tools/water-intake-calculator \
  -H "Content-Type: application/json" \
  -d '[]'

Example response

{
    "data": {
        "litres": 2.7,
        "fluid_ounces": 91
    },
    "meta": {
        "tool": "water-intake-calculator"
    }
}

Waist-to-Height Ratio Calculator

Calculate your waist-to-height ratio as an adult screening measure.

POST https://synsi.nl/api/v1/tools/waist-to-height-ratio

Parameters

Parameter Type Required Description
waist number no waist
default: 80
height number no height
default: 170
unit string no unit
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/waist-to-height-ratio \
  -H "Content-Type: application/json" \
  -d '{"waist":80,"height":170}'

Example response

{
    "data": {
        "ratio": 0.47,
        "category": "lower"
    },
    "meta": {
        "tool": "waist-to-height-ratio"
    }
}

Lean Body Mass Calculator

Estimate fat-free mass from body weight and body-fat percentage.

POST https://synsi.nl/api/v1/tools/lean-body-mass-calculator

Parameters

Parameter Type Required Description
weight number no weight
default: 70
body_fat number no body_fat
default: 20
unit string no unit
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/lean-body-mass-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"body_fat":20}'

Example response

{
    "data": {
        "lean_mass": 56,
        "fat_mass": 14,
        "unit": "kg"
    },
    "meta": {
        "tool": "lean-body-mass-calculator"
    }
}

Calories Burned Calculator

Estimate energy use from body weight, activity and exercise duration.

POST https://synsi.nl/api/v1/tools/calories-burned-calculator

Parameters

Parameter Type Required Description
weight number no weight
default: 70
minutes number no minutes
default: 30
activity string no activity
walking · cycling · running · swimming · strength_training
default: walking
unit string no unit
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/calories-burned-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":70,"minutes":30}'

Example response

{
    "data": {
        "total_kcal": 129,
        "active_kcal": 92
    },
    "meta": {
        "tool": "calories-burned-calculator"
    }
}

Running Pace Calculator

Find your pace per kilometre and mile from distance and finish time.

POST https://synsi.nl/api/v1/tools/running-pace-calculator

Parameters

Parameter Type Required Description
distance number no distance
default: 5
hours integer no hours
default: 0
minutes integer no minutes
default: 25
seconds integer no seconds
default: 0
unit string no unit
km · mi
default: km

Example request

curl -X POST https://synsi.nl/api/v1/tools/running-pace-calculator \
  -H "Content-Type: application/json" \
  -d '{"distance":5,"hours":0,"minutes":25,"seconds":0}'

Example response

{
    "data": {
        "pace_seconds_per_km": 300,
        "pace_seconds_per_mile": 482.8,
        "speed_kmh": 12
    },
    "meta": {
        "tool": "running-pace-calculator"
    }
}

One Rep Max Calculator

Estimate a one-repetition maximum from the weight and repetitions completed.

POST https://synsi.nl/api/v1/tools/one-rep-max-calculator

Parameters

Parameter Type Required Description
weight number no weight
default: 60
reps integer no reps
default: 8
unit string no unit
kg · lb
default: kg

Example request

curl -X POST https://synsi.nl/api/v1/tools/one-rep-max-calculator \
  -H "Content-Type: application/json" \
  -d '{"weight":60,"reps":8}'

Example response

{
    "data": {
        "epley": 76,
        "brzycki": 74.5,
        "unit": "kg"
    },
    "meta": {
        "tool": "one-rep-max-calculator"
    }
}

Heart Rate Zone Calculator

Estimate five training heart-rate zones from age-predicted maximum heart rate.

POST https://synsi.nl/api/v1/tools/heart-rate-zone-calculator

Parameters

Parameter Type Required Description
age integer no age
default: 30

Example request

curl -X POST https://synsi.nl/api/v1/tools/heart-rate-zone-calculator \
  -H "Content-Type: application/json" \
  -d '{"age":30}'

Example response

{
    "data": {
        "max_hr": 187,
        "zones": [
            {
                "zone": 1,
                "min": 94,
                "max": 112
            },
            {
                "zone": 2,
                "min": 112,
                "max": 131
            },
            {
                "zone": 3,
                "min": 131,
                "max": 150
            },
            {
                "zone": 4,
                "min": 150,
                "max": 168
            },
            {
                "zone": 5,
                "min": 168,
                "max": 187
            }
        ]
    },
    "meta": {
        "tool": "heart-rate-zone-calculator"
    }
}

Sleep Calculator

Choose a wake time and see bedtimes allowing for 7, 8 or 9 hours of sleep.

POST https://synsi.nl/api/v1/tools/sleep-calculator

Parameters

Parameter Type Required Description
wake_time string no Wake time in 24-hour HH:MM format.
default: 07:00
latency integer no latency
default: 15

Example request

curl -X POST https://synsi.nl/api/v1/tools/sleep-calculator \
  -H "Content-Type: application/json" \
  -d '{"latency":15}'

Example response

{
    "data": {
        "bedtimes": [
            {
                "hours": 7,
                "time": "23:45"
            },
            {
                "hours": 8,
                "time": "22:45"
            },
            {
                "hours": 9,
                "time": "21:45"
            }
        ]
    },
    "meta": {
        "tool": "sleep-calculator"
    }
}

Due Date Calculator

Estimate a pregnancy due date from the first day of the last menstrual period.

POST https://synsi.nl/api/v1/tools/due-date-calculator

Parameters

Parameter Type Required Description
lmp_date string (date) yes
cycle_length integer no cycle_length
default: 28

Example request

curl -X POST https://synsi.nl/api/v1/tools/due-date-calculator \
  -H "Content-Type: application/json" \
  -d '{"lmp_date":"2026-01-01","cycle_length":28}'

Example response

{
    "data": {
        "due_date": "2026-10-08"
    },
    "meta": {
        "tool": "due-date-calculator"
    }
}

Ovulation Calculator

Estimate ovulation and a fertile window from period date and cycle length.

POST https://synsi.nl/api/v1/tools/ovulation-calculator

Parameters

Parameter Type Required Description
lmp_date string (date) yes
cycle_length integer no cycle_length
default: 28

Example request

curl -X POST https://synsi.nl/api/v1/tools/ovulation-calculator \
  -H "Content-Type: application/json" \
  -d '{"lmp_date":"2026-01-01","cycle_length":28}'

Example response

{
    "data": {
        "ovulation_date": "2026-01-15",
        "fertile_start": "2026-01-10",
        "fertile_end": "2026-01-16"
    },
    "meta": {
        "tool": "ovulation-calculator"
    }
}

Pregnancy Weight Gain Calculator

Compare current gain with a singleton pregnancy reference range based on pre-pregnancy BMI.

POST https://synsi.nl/api/v1/tools/pregnancy-weight-gain-calculator

Parameters

Parameter Type Required Description
height number no height
default: 165
prepregnancy_weight number no prepregnancy_weight
default: 65
current_weight number no current_weight
default: 70
unit string no unit
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/pregnancy-weight-gain-calculator \
  -H "Content-Type: application/json" \
  -d '{"height":165,"prepregnancy_weight":65,"current_weight":70}'

Example response

{
    "data": {
        "bmi": 23.9,
        "category": "healthy",
        "gain_min": 11.3,
        "gain_max": 15.9,
        "gain_so_far": 5,
        "unit": "kg"
    },
    "meta": {
        "tool": "pregnancy-weight-gain-calculator"
    }
}

Vitamin & Mineral Intake Calculator

Vitamin and mineral intake calculator: see the US RDA or AI and the EU PRI or AI with upper limits for 23 nutrients, by age, sex, pregnancy and breastfeeding.

POST https://synsi.nl/api/v1/tools/vitamin-mineral-intake-calculator

Parameters

Parameter Type Required Description
age integer no Age in years. Reference values cover adults aged 19 and over.
default: 35
sex string no Sex used to select reference values.
female · male
default: female
status string no Pregnancy or lactation; female profile only.
none · pregnant · lactating
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/vitamin-mineral-intake-calculator \
  -H "Content-Type: application/json" \
  -d '{"age":35}'

Example response

{
    "data": {
        "rows": [
            {
                "nutrient": "vitamin-a",
                "group": "vitamin",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 700,
                    "ri_note": null,
                    "ul": 3000,
                    "ul_type": "ul",
                    "ul_note": "preformed"
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 650,
                    "ri_note": null,
                    "ul": 3000,
                    "ul_type": "ul",
                    "ul_note": "preformed"
                }
            },
            {
                "nutrient": "thiamin",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1.1,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": null,
                    "ri_note": "per_energy_thiamin",
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "riboflavin",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1.1,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 1.6,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "niacin",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 14,
                    "ri_note": null,
                    "ul": 35,
                    "ul_type": "ul",
                    "ul_note": "supplemental"
                },
                "efsa": {
                    "type": "PRI",
                    "ri": null,
                    "ri_note": "per_energy_niacin",
                    "ul": 10,
                    "ul_type": "ul",
                    "ul_note": "nicotinic_acid"
                }
            },
            {
                "nutrient": "pantothenic-acid",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "AI",
                    "ri": 5,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 5,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "vitamin-b6",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1.3,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 1.6,
                    "ri_note": null,
                    "ul": 12,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "biotin",
                "group": "vitamin",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "AI",
                    "ri": 30,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 40,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "folate",
                "group": "vitamin",
                "unit": "µg",
                "dfe": true,
                "nih": {
                    "type": "RDA",
                    "ri": 400,
                    "ri_note": null,
                    "ul": 1000,
                    "ul_type": "ul",
                    "ul_note": "folic_acid"
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 330,
                    "ri_note": null,
                    "ul": 1000,
                    "ul_type": "ul",
                    "ul_note": "folic_acid"
                }
            },
            {
                "nutrient": "vitamin-b12",
                "group": "vitamin",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 2.4,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 4,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "vitamin-c",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 75,
                    "ri_note": null,
                    "ul": 2000,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 95,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "vitamin-d",
                "group": "vitamin",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "vitamin-e",
                "group": "vitamin",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 1000,
                    "ul_type": "ul",
                    "ul_note": "supplemental"
                },
                "efsa": {
                    "type": "AI",
                    "ri": 11,
                    "ri_note": null,
                    "ul": 300,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "vitamin-k",
                "group": "vitamin",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "AI",
                    "ri": 90,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 70,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "calcium",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1000,
                    "ri_note": null,
                    "ul": 2500,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 950,
                    "ri_note": null,
                    "ul": 2500,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "magnesium",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 320,
                    "ri_note": null,
                    "ul": 350,
                    "ul_type": "ul",
                    "ul_note": "supplemental"
                },
                "efsa": {
                    "type": "AI",
                    "ri": 300,
                    "ri_note": null,
                    "ul": 250,
                    "ul_type": "ul",
                    "ul_note": "supplemental"
                }
            },
            {
                "nutrient": "iron",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 18,
                    "ri_note": null,
                    "ul": 45,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 16,
                    "ri_note": "iron_menopause",
                    "ul": 40,
                    "ul_type": "safe_level",
                    "ul_note": null
                }
            },
            {
                "nutrient": "zinc",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 8,
                    "ri_note": null,
                    "ul": 40,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 9.3,
                    "ri_note": "zinc_phytate",
                    "ul": 25,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "selenium",
                "group": "mineral",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 55,
                    "ri_note": null,
                    "ul": 400,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 70,
                    "ri_note": null,
                    "ul": 255,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "iodine",
                "group": "mineral",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 150,
                    "ri_note": null,
                    "ul": 1100,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 150,
                    "ri_note": null,
                    "ul": 600,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "copper",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 0.9,
                    "ri_note": null,
                    "ul": 10,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 1.3,
                    "ri_note": null,
                    "ul": 5,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "manganese",
                "group": "mineral",
                "unit": "mg",
                "dfe": false,
                "nih": {
                    "type": "AI",
                    "ri": 1.8,
                    "ri_note": null,
                    "ul": 11,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 3,
                    "ri_note": null,
                    "ul": 8,
                    "ul_type": "safe_level",
                    "ul_note": null
                }
            },
            {
                "nutrient": "chromium",
                "group": "mineral",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "AI",
                    "ri": 25,
                    "ri_note": null,
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": null,
                    "ri": null,
                    "ri_note": "chromium_none",
                    "ul": null,
                    "ul_type": "ul",
                    "ul_note": null
                }
            },
            {
                "nutrient": "molybdenum",
                "group": "mineral",
                "unit": "µg",
                "dfe": false,
                "nih": {
                    "type": "RDA",
                    "ri": 45,
                    "ri_note": null,
                    "ul": 2000,
                    "ul_type": "ul",
                    "ul_note": null
                },
                "efsa": {
                    "type": "AI",
                    "ri": 65,
                    "ri_note": null,
                    "ul": 600,
                    "ul_type": "ul",
                    "ul_note": null
                }
            }
        ]
    },
    "meta": {
        "tool": "vitamin-mineral-intake-calculator"
    }
}

Length Converter

Free length converter for metres, centimetres, feet, inches, yards, miles, kilometres and nautical miles. Exact factors and instant results.

POST https://synsi.nl/api/v1/tools/length-converter

Parameters

Parameter Type Required Description
category string no
length
default: length
value number yes
from string yes
mm · cm · dm · m · km · in · ft · yd · mi · nmi
to string yes
mm · cm · dm · m · km · in · ft · yd · mi · nmi

Example request

curl -X POST https://synsi.nl/api/v1/tools/length-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"m","to":"ft"}'

Example response

{
    "data": {
        "result": 32.8083989501
    },
    "meta": {
        "tool": "length-converter"
    }
}

Supplement Stack Calculator

Supplement stack calculator: add up vitamins and minerals from all your products, spot nutrients you take twice and compare totals with US and EU upper limits.

POST https://synsi.nl/api/v1/tools/supplement-stack-calculator

Parameters

Parameter Type Required Description
products string yes One product per line: "Name: nutrient amount unit, …" or "nutrient amount unit". Units: mg, µg (mcg), g, IU.
age integer no Age in years. Reference values cover adults aged 19 and over.
default: 35
sex string no Sex used to select reference values.
female · male
default: female
status string no Pregnancy or lactation; female profile only.
none · pregnant · lactating
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/supplement-stack-calculator \
  -H "Content-Type: application/json" \
  -d '{"products":"Vitamin D3: 25 µg\nMultivitamin: vitamin D 10 µg, zinc 10 mg, vitamin B6 2 mg\nMagnesium citrate: 750 mg\nZinc: 15 mg","age":35}'

Example response

{
    "data": {
        "rows": [
            {
                "nutrient": "vitamin-b6",
                "unit": "mg",
                "total": 2,
                "dfe": null,
                "sources": [
                    "Multivitamin"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1.3,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 153.8,
                    "ul_percent": 2
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 1.6,
                    "ri_note": null,
                    "ul": 12,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 125,
                    "ul_percent": 16.7
                }
            },
            {
                "nutrient": "vitamin-d",
                "unit": "µg",
                "total": 35,
                "dfe": null,
                "sources": [
                    "Vitamin D3",
                    "Multivitamin"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 233.3,
                    "ul_percent": 35
                },
                "efsa": {
                    "type": "AI",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 233.3,
                    "ul_percent": 35
                }
            },
            {
                "nutrient": "magnesium",
                "unit": "mg",
                "total": 121.2,
                "dfe": null,
                "sources": [
                    "Magnesium citrate"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 320,
                    "ri_note": null,
                    "ul": 350,
                    "ul_type": "ul",
                    "ul_note": "supplemental",
                    "ri_percent": 37.9,
                    "ul_percent": 34.6
                },
                "efsa": {
                    "type": "AI",
                    "ri": 300,
                    "ri_note": null,
                    "ul": 250,
                    "ul_type": "ul",
                    "ul_note": "supplemental",
                    "ri_percent": 40.4,
                    "ul_percent": 48.5
                }
            },
            {
                "nutrient": "zinc",
                "unit": "mg",
                "total": 25,
                "dfe": null,
                "sources": [
                    "Multivitamin",
                    "Zinc"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 8,
                    "ri_note": null,
                    "ul": 40,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 312.5,
                    "ul_percent": 62.5
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 9.3,
                    "ri_note": "zinc_phytate",
                    "ul": 25,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 268.8,
                    "ul_percent": 100
                }
            }
        ],
        "duplicates": [
            "vitamin-d",
            "zinc"
        ],
        "above_ul": [],
        "conversions": [
            {
                "product": "Magnesium citrate",
                "compound": "magnesium-citrate",
                "amount": 750,
                "elemental": 121.2
            }
        ],
        "unrecognized": []
    },
    "meta": {
        "tool": "supplement-stack-calculator"
    }
}

Weight Converter

Free weight converter for kilograms, grams, pounds, ounces, stone and tonnes. Exact factors for kg to lb, lb to kg and stone to kg conversions.

POST https://synsi.nl/api/v1/tools/weight-converter

Parameters

Parameter Type Required Description
category string no
weight
default: weight
value number yes
from string yes
mg · g · kg · t · oz · lb · st
to string yes
mg · g · kg · t · oz · lb · st

Example request

curl -X POST https://synsi.nl/api/v1/tools/weight-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"kg","to":"lb"}'

Example response

{
    "data": {
        "result": 22.0462262185
    },
    "meta": {
        "tool": "weight-converter"
    }
}

Supplement Label Analyzer

Supplement label analyzer: paste a Supplement Facts label to see each vitamin and mineral against US and EU upper limits, including overlap with other products.

POST https://synsi.nl/api/v1/tools/supplement-label-analyzer

Parameters

Parameter Type Required Description
label string yes Supplement facts text, one nutrient per line.
servings number no Servings per day.
default: 1
other string no Optional: other products you take, in the supplement stack format.
default:
age integer no Age in years. Reference values cover adults aged 19 and over.
default: 35
sex string no Sex used to select reference values.
female · male
default: female
status string no Pregnancy or lactation; female profile only.
none · pregnant · lactating
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/supplement-label-analyzer \
  -H "Content-Type: application/json" \
  -d '{"label":"Supplement Facts\nServing size: 1 tablet\nVitamin D (as cholecalciferol) 25 µg (1,000 IU)\nVitamin B6 (as pyridoxine HCl) 2 mg\nMagnesium (as magnesium citrate) 200 mg\nZinc (as zinc gluconate) 15 mg","servings":1,"age":35}'

Example response

{
    "data": {
        "rows": [
            {
                "nutrient": "vitamin-b6",
                "unit": "mg",
                "total": 2,
                "dfe": null,
                "sources": [
                    "label"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 1.3,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 153.8,
                    "ul_percent": 2
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 1.6,
                    "ri_note": null,
                    "ul": 12,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 125,
                    "ul_percent": 16.7
                }
            },
            {
                "nutrient": "vitamin-d",
                "unit": "µg",
                "total": 25,
                "dfe": null,
                "sources": [
                    "label"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 166.7,
                    "ul_percent": 25
                },
                "efsa": {
                    "type": "AI",
                    "ri": 15,
                    "ri_note": null,
                    "ul": 100,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 166.7,
                    "ul_percent": 25
                }
            },
            {
                "nutrient": "magnesium",
                "unit": "mg",
                "total": 200,
                "dfe": null,
                "sources": [
                    "label"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 320,
                    "ri_note": null,
                    "ul": 350,
                    "ul_type": "ul",
                    "ul_note": "supplemental",
                    "ri_percent": 62.5,
                    "ul_percent": 57.1
                },
                "efsa": {
                    "type": "AI",
                    "ri": 300,
                    "ri_note": null,
                    "ul": 250,
                    "ul_type": "ul",
                    "ul_note": "supplemental",
                    "ri_percent": 66.7,
                    "ul_percent": 80
                }
            },
            {
                "nutrient": "zinc",
                "unit": "mg",
                "total": 15,
                "dfe": null,
                "sources": [
                    "label"
                ],
                "above_ul": false,
                "nih": {
                    "type": "RDA",
                    "ri": 8,
                    "ri_note": null,
                    "ul": 40,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 187.5,
                    "ul_percent": 37.5
                },
                "efsa": {
                    "type": "PRI",
                    "ri": 9.3,
                    "ri_note": "zinc_phytate",
                    "ul": 25,
                    "ul_type": "ul",
                    "ul_note": null,
                    "ri_percent": 161.3,
                    "ul_percent": 60
                }
            }
        ],
        "duplicates": [],
        "above_ul": [],
        "conversions": [],
        "unrecognized": []
    },
    "meta": {
        "tool": "supplement-label-analyzer"
    }
}

Temperature Converter

Free temperature converter for Celsius, Fahrenheit and Kelvin. See the formulas, oven temperatures and body temperature conversions instantly.

POST https://synsi.nl/api/v1/tools/temperature-converter

Parameters

Parameter Type Required Description
category string no
temperature
default: temperature
value number yes
from string yes
C · F · K
to string yes
C · F · K

Example request

curl -X POST https://synsi.nl/api/v1/tools/temperature-converter \
  -H "Content-Type: application/json" \
  -d '{"value":20,"from":"C","to":"F"}'

Example response

{
    "data": {
        "result": 68
    },
    "meta": {
        "tool": "temperature-converter"
    }
}

Supplement Dose Calculator

Supplement dose calculator: enter a vitamin or mineral, the amount per serving and servings per day to see your intake as a share of the RDA and upper limit.

POST https://synsi.nl/api/v1/tools/supplement-dose-calculator

Parameters

Parameter Type Required Description
nutrient string no
vitamin-a · thiamin · riboflavin · niacin · pantothenic-acid · vitamin-b6 · biotin · folate · vitamin-b12 · vitamin-c · vitamin-d · vitamin-e · vitamin-k · calcium · magnesium · iron · zinc · selenium · iodine · copper · manganese · chromium · molybdenum
default: vitamin-d
amount number no Amount per serving.
default: 25
unit string no
mg · mcg · g · IU
default: mcg
servings number no Servings per day.
default: 1
age integer no Age in years. Reference values cover adults aged 19 and over.
default: 35
sex string no Sex used to select reference values.
female · male
default: female
status string no Pregnancy or lactation; female profile only.
none · pregnant · lactating
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/supplement-dose-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":25,"servings":1,"age":35}'

Example response

{
    "data": {
        "daily": 25,
        "unit": "µg",
        "daily_iu": 1000,
        "row": {
            "nutrient": "vitamin-d",
            "unit": "µg",
            "total": 25,
            "dfe": null,
            "sources": [
                "dose"
            ],
            "above_ul": false,
            "nih": {
                "type": "RDA",
                "ri": 15,
                "ri_note": null,
                "ul": 100,
                "ul_type": "ul",
                "ul_note": null,
                "ri_percent": 166.7,
                "ul_percent": 25
            },
            "efsa": {
                "type": "AI",
                "ri": 15,
                "ri_note": null,
                "ul": 100,
                "ul_type": "ul",
                "ul_note": null,
                "ri_percent": 166.7,
                "ul_percent": 25
            }
        }
    },
    "meta": {
        "tool": "supplement-dose-calculator"
    }
}

Volume Converter

Free volume converter for litres, millilitres, US and UK gallons, cups, pints, quarts, fluid ounces, tablespoons, teaspoons and cubic metres.

POST https://synsi.nl/api/v1/tools/volume-converter

Parameters

Parameter Type Required Description
category string no
volume
default: volume
value number yes
from string yes
ml · cl · dl · l · m3 · tsp · tbsp · floz · cup · pt · qt · gal · ukgal
to string yes
ml · cl · dl · l · m3 · tsp · tbsp · floz · cup · pt · qt · gal · ukgal

Example request

curl -X POST https://synsi.nl/api/v1/tools/volume-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"l","to":"gal"}'

Example response

{
    "data": {
        "result": 2.64172052358
    },
    "meta": {
        "tool": "volume-converter"
    }
}

Vitamin D Calculator

Vitamin D calculator: convert IU to µg, add food and other supplements, and compare your daily vitamin D with the US RDA, EU AI and the 100 µg upper limit.

POST https://synsi.nl/api/v1/tools/vitamin-d-calculator

Parameters

Parameter Type Required Description
amount number no Vitamin D per serving.
default: 1000
unit string no
IU · mcg
default: IU
servings number no Servings per day.
default: 1
other_ug number no Vitamin D from food and other supplements, in µg per day.
default: 0
age integer no Age in years. Reference values cover adults aged 19 and over.
default: 35
sex string no Sex used to select reference values.
female · male
default: female
status string no Pregnancy or lactation; female profile only.
none · pregnant · lactating
default: none

Example request

curl -X POST https://synsi.nl/api/v1/tools/vitamin-d-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":1000,"servings":1,"age":35}'

Example response

{
    "data": {
        "supplement_ug": 25,
        "supplement_iu": 1000,
        "total_ug": 25,
        "total_iu": 1000,
        "row": {
            "nutrient": "vitamin-d",
            "unit": "µg",
            "total": 25,
            "dfe": null,
            "sources": [
                "total"
            ],
            "above_ul": false,
            "nih": {
                "type": "RDA",
                "ri": 15,
                "ri_note": null,
                "ul": 100,
                "ul_type": "ul",
                "ul_note": null,
                "ri_percent": 166.7,
                "ul_percent": 25
            },
            "efsa": {
                "type": "AI",
                "ri": 15,
                "ri_note": null,
                "ul": 100,
                "ul_type": "ul",
                "ul_note": null,
                "ri_percent": 166.7,
                "ul_percent": 25
            }
        }
    },
    "meta": {
        "tool": "vitamin-d-calculator"
    }
}

Area Converter

Free area converter for square metres, square feet, acres, hectares, square kilometres, square miles, square yards and square inches. Exact results.

POST https://synsi.nl/api/v1/tools/area-converter

Parameters

Parameter Type Required Description
category string no
area
default: area
value number yes
from string yes
mm2 · cm2 · m2 · ha · km2 · in2 · ft2 · yd2 · ac · mi2
to string yes
mm2 · cm2 · m2 · ha · km2 · in2 · ft2 · yd2 · ac · mi2

Example request

curl -X POST https://synsi.nl/api/v1/tools/area-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"m2","to":"ft2"}'

Example response

{
    "data": {
        "result": 107.639104167
    },
    "meta": {
        "tool": "area-converter"
    }
}

Elemental Mineral Calculator

Elemental mineral calculator: convert the weight of magnesium citrate, calcium carbonate, zinc gluconate, ferrous sulfate and more into the elemental amount.

POST https://synsi.nl/api/v1/tools/elemental-mineral-calculator

Parameters

Parameter Type Required Description
compound string no
magnesium-oxide · magnesium-citrate · magnesium-glycinate · magnesium-malate · magnesium-taurate · magnesium-l-threonate · magnesium-chloride · magnesium-sulfate · magnesium-carbonate · magnesium-lactate · magnesium-hydroxide · calcium-carbonate · calcium-citrate · calcium-lactate · calcium-gluconate · calcium-phosphate · zinc-gluconate · zinc-citrate · zinc-picolinate · zinc-bisglycinate · zinc-oxide · zinc-sulfate · zinc-acetate · ferrous-sulfate · ferrous-sulfate-dried · ferrous-fumarate · ferrous-gluconate · ferrous-bisglycinate
default: magnesium-citrate
amount number no Weight of the compound per serving, in mg.
default: 500
servings number no Servings per day.
default: 1

Example request

curl -X POST https://synsi.nl/api/v1/tools/elemental-mineral-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":500,"servings":1}'

Example response

{
    "data": {
        "nutrient": "magnesium",
        "formula": "Mg3(C6H5O7)2",
        "fraction_percent": 16.16,
        "elemental_mg": 80.8,
        "daily_elemental_mg": 80.8,
        "nih": {
            "ul": 350,
            "ul_type": "ul",
            "ul_note": "supplemental",
            "ul_percent": 23.1
        },
        "efsa": {
            "ul": 250,
            "ul_type": "ul",
            "ul_note": "supplemental",
            "ul_percent": 32.3
        }
    },
    "meta": {
        "tool": "elemental-mineral-calculator"
    }
}

Speed Converter

Free speed converter for kilometres per hour, miles per hour, knots, metres per second and feet per second. Exact results for driving and sailing.

POST https://synsi.nl/api/v1/tools/speed-converter

Parameters

Parameter Type Required Description
category string no
speed
default: speed
value number yes
from string yes
m/s · km/h · mph · kn · ft/s
to string yes
m/s · km/h · mph · kn · ft/s

Example request

curl -X POST https://synsi.nl/api/v1/tools/speed-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"km/h","to":"mph"}'

Example response

{
    "data": {
        "result": 6.21371192237
    },
    "meta": {
        "tool": "speed-converter"
    }
}

Magnesium Calculator

Magnesium calculator: find the elemental magnesium in magnesium citrate, glycinate, oxide, malate, taurate and threonate, and compare it with the upper limit.

POST https://synsi.nl/api/v1/tools/magnesium-calculator

Parameters

Parameter Type Required Description
compound string no
magnesium-oxide · magnesium-citrate · magnesium-glycinate · magnesium-malate · magnesium-taurate · magnesium-l-threonate · magnesium-chloride · magnesium-sulfate · magnesium-carbonate · magnesium-lactate · magnesium-hydroxide
default: magnesium-citrate
amount number no Weight of the compound per serving, in mg.
default: 500
servings number no Servings per day.
default: 1

Example request

curl -X POST https://synsi.nl/api/v1/tools/magnesium-calculator \
  -H "Content-Type: application/json" \
  -d '{"amount":500,"servings":1}'

Example response

{
    "data": {
        "nutrient": "magnesium",
        "formula": "Mg3(C6H5O7)2",
        "fraction_percent": 16.16,
        "elemental_mg": 80.8,
        "daily_elemental_mg": 80.8,
        "nih": {
            "ul": 350,
            "ul_type": "ul",
            "ul_note": "supplemental",
            "ul_percent": 23.1
        },
        "efsa": {
            "ul": 250,
            "ul_type": "ul",
            "ul_note": "supplemental",
            "ul_percent": 32.3
        }
    },
    "meta": {
        "tool": "magnesium-calculator"
    }
}

Time Converter

Free time converter for milliseconds, seconds, minutes, hours, days, weeks and years. Convert hours to minutes, days to hours and more instantly.

POST https://synsi.nl/api/v1/tools/time-converter

Parameters

Parameter Type Required Description
category string no
time
default: time
value number yes
from string yes
ms · s · min · h · d · wk · yr
to string yes
ms · s · min · h · d · wk · yr

Example request

curl -X POST https://synsi.nl/api/v1/tools/time-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"h","to":"min"}'

Example response

{
    "data": {
        "result": 600
    },
    "meta": {
        "tool": "time-converter"
    }
}

IU Converter

IU converter for vitamins: convert international units to micrograms or milligrams and back for vitamin D, vitamin A (retinol, beta-carotene) and vitamin E.

POST https://synsi.nl/api/v1/tools/vitamin-unit-converter

Parameters

Parameter Type Required Description
form string no
vitamin-d · vitamin-a-retinol · vitamin-a-beta-carotene · vitamin-e-natural · vitamin-e-synthetic
default: vitamin-d
value number no
default: 1000
direction string no
iu_to_mass · mass_to_iu
default: iu_to_mass

Example request

curl -X POST https://synsi.nl/api/v1/tools/vitamin-unit-converter \
  -H "Content-Type: application/json" \
  -d '{"value":1000}'

Example response

{
    "data": {
        "result": 25,
        "unit": "µg",
        "per_iu": 0.025
    },
    "meta": {
        "tool": "vitamin-unit-converter"
    }
}

Data Storage Converter

Free data storage converter for bits, bytes, KB, MB, GB, TB, PB and binary KiB, MiB, GiB and TiB. See why a 1 TB drive shows 931 GB.

POST https://synsi.nl/api/v1/tools/data-storage-converter

Parameters

Parameter Type Required Description
category string no
data
default: data
value number yes
from string yes
bit · Kbit · Mbit · Gbit · B · KB · MB · GB · TB · PB · KiB · MiB · GiB · TiB
to string yes
bit · Kbit · Mbit · Gbit · B · KB · MB · GB · TB · PB · KiB · MiB · GiB · TiB

Example request

curl -X POST https://synsi.nl/api/v1/tools/data-storage-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"GB","to":"GiB"}'

Example response

{
    "data": {
        "result": 9.31322574615
    },
    "meta": {
        "tool": "data-storage-converter"
    }
}

Pressure Converter

Free pressure converter for bar, psi, pascal, kilopascal, megapascal, millibar, atmospheres and torr. Ideal for tyre, weather and hydraulic pressure.

POST https://synsi.nl/api/v1/tools/pressure-converter

Parameters

Parameter Type Required Description
category string no
pressure
default: pressure
value number yes
from string yes
Pa · kPa · MPa · bar · mbar · psi · atm · torr
to string yes
Pa · kPa · MPa · bar · mbar · psi · atm · torr

Example request

curl -X POST https://synsi.nl/api/v1/tools/pressure-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"bar","to":"psi"}'

Example response

{
    "data": {
        "result": 145.03773773
    },
    "meta": {
        "tool": "pressure-converter"
    }
}

Energy Converter

Free energy converter for joules, kilojoules, megajoules, watt-hours, kilowatt-hours, calories, kilocalories and BTU. Exact factors, instant results.

POST https://synsi.nl/api/v1/tools/energy-converter

Parameters

Parameter Type Required Description
category string no
energy
default: energy
value number yes
from string yes
J · kJ · MJ · Wh · kWh · cal · kcal · BTU
to string yes
J · kJ · MJ · Wh · kWh · cal · kcal · BTU

Example request

curl -X POST https://synsi.nl/api/v1/tools/energy-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"kWh","to":"MJ"}'

Example response

{
    "data": {
        "result": 36
    },
    "meta": {
        "tool": "energy-converter"
    }
}

Power Converter

Free power converter for watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS) and BTU per hour. Exact, instant results.

POST https://synsi.nl/api/v1/tools/power-converter

Parameters

Parameter Type Required Description
category string no
power
default: power
value number yes
from string yes
W · kW · MW · hp · metric-hp · BTU/h
to string yes
W · kW · MW · hp · metric-hp · BTU/h

Example request

curl -X POST https://synsi.nl/api/v1/tools/power-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"kW","to":"hp"}'

Example response

{
    "data": {
        "result": 13.410220896
    },
    "meta": {
        "tool": "power-converter"
    }
}

Frequency Converter

Free frequency converter for hertz, kilohertz, megahertz, gigahertz, terahertz and revolutions per minute (RPM). Instant and exact results.

POST https://synsi.nl/api/v1/tools/frequency-converter

Parameters

Parameter Type Required Description
category string no
frequency
default: frequency
value number yes
from string yes
Hz · kHz · MHz · GHz · THz · rpm
to string yes
Hz · kHz · MHz · GHz · THz · rpm

Example request

curl -X POST https://synsi.nl/api/v1/tools/frequency-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"MHz","to":"kHz"}'

Example response

{
    "data": {
        "result": 10000
    },
    "meta": {
        "tool": "frequency-converter"
    }
}

Angle Converter

Free angle converter for degrees, radians, gradians, arcminutes and arcseconds. Convert degrees to radians and back with the exact formula.

POST https://synsi.nl/api/v1/tools/angle-converter

Parameters

Parameter Type Required Description
category string no
angle
default: angle
value number yes
from string yes
rad · deg · arcmin · arcsec · grad
to string yes
rad · deg · arcmin · arcsec · grad

Example request

curl -X POST https://synsi.nl/api/v1/tools/angle-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"deg","to":"rad"}'

Example response

{
    "data": {
        "result": 0.174532925199
    },
    "meta": {
        "tool": "angle-converter"
    }
}

Force Converter

Free force converter for newtons, kilonewtons, pound-force, kilogram-force and dynes. Convert N to lbf, kgf to N and more with exact definitions.

POST https://synsi.nl/api/v1/tools/force-converter

Parameters

Parameter Type Required Description
category string no
force
default: force
value number yes
from string yes
N · kN · dyn · kgf · lbf
to string yes
N · kN · dyn · kgf · lbf

Example request

curl -X POST https://synsi.nl/api/v1/tools/force-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"N","to":"lbf"}'

Example response

{
    "data": {
        "result": 2.248089431
    },
    "meta": {
        "tool": "force-converter"
    }
}

Torque Converter

Free torque converter for newton-metres, kilonewton-metres, pound-feet and pound-inches. Convert engine torque and torque wrench settings exactly.

POST https://synsi.nl/api/v1/tools/torque-converter

Parameters

Parameter Type Required Description
category string no
torque
default: torque
value number yes
from string yes
Nm · kNm · lb-ft · lb-in
to string yes
Nm · kNm · lb-ft · lb-in

Example request

curl -X POST https://synsi.nl/api/v1/tools/torque-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"Nm","to":"lb-ft"}'

Example response

{
    "data": {
        "result": 7.37562149277
    },
    "meta": {
        "tool": "torque-converter"
    }
}

Fuel Economy Converter

Free fuel economy converter for litres per 100 km, kilometres per litre, US MPG and UK (imperial) MPG. Compare car fuel consumption worldwide.

POST https://synsi.nl/api/v1/tools/fuel-economy-converter

Parameters

Parameter Type Required Description
category string no
fuel-economy
default: fuel-economy
value number yes
from string yes
km/L · L/100km · mpg-us · mpg-uk
to string yes
km/L · L/100km · mpg-us · mpg-uk

Example request

curl -X POST https://synsi.nl/api/v1/tools/fuel-economy-converter \
  -H "Content-Type: application/json" \
  -d '{"value":8,"from":"L/100km","to":"mpg-us"}'

Example response

{
    "data": {
        "result": 29.4018229167
    },
    "meta": {
        "tool": "fuel-economy-converter"
    }
}

Density Converter

Free density converter for kilograms per cubic metre, grams per cubic centimetre, grams per millilitre, pounds per cubic foot and pounds per US gallon.

POST https://synsi.nl/api/v1/tools/density-converter

Parameters

Parameter Type Required Description
category string no
density
default: density
value number yes
from string yes
kg/m3 · g/cm3 · g/ml · lb/ft3 · lb/gal-us
to string yes
kg/m3 · g/cm3 · g/ml · lb/ft3 · lb/gal-us

Example request

curl -X POST https://synsi.nl/api/v1/tools/density-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"g/cm3","to":"kg/m3"}'

Example response

{
    "data": {
        "result": 10000
    },
    "meta": {
        "tool": "density-converter"
    }
}

Acceleration Converter

Free acceleration converter for metres per second squared, standard gravity (g) and feet per second squared. Convert g-force to m/s² and back.

POST https://synsi.nl/api/v1/tools/acceleration-converter

Parameters

Parameter Type Required Description
category string no
acceleration
default: acceleration
value number yes
from string yes
m/s2 · g0 · ft/s2
to string yes
m/s2 · g0 · ft/s2

Example request

curl -X POST https://synsi.nl/api/v1/tools/acceleration-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"g0","to":"m/s2"}'

Example response

{
    "data": {
        "result": 98.0665
    },
    "meta": {
        "tool": "acceleration-converter"
    }
}

Illuminance Converter

Free illuminance converter for lux, kilolux, foot-candles and phot. Convert lux to foot-candles for lighting design, photography and plant grow lights.

POST https://synsi.nl/api/v1/tools/illuminance-converter

Parameters

Parameter Type Required Description
category string no
illuminance
default: illuminance
value number yes
from string yes
lx · klx · fc · phot
to string yes
lx · klx · fc · phot

Example request

curl -X POST https://synsi.nl/api/v1/tools/illuminance-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"lx","to":"fc"}'

Example response

{
    "data": {
        "result": 0.9290304
    },
    "meta": {
        "tool": "illuminance-converter"
    }
}

Electrical Units Converter

Free electrical units converter for volts, millivolts, kilovolts, amps, milliamps, ohms, kilohms, megohms, watts and kilowatts. Includes Ohm’s law.

POST https://synsi.nl/api/v1/tools/electrical-units-converter

Parameters

Parameter Type Required Description
category string no
voltage · current · resistance · power
default: voltage
value number yes
from string yes
W · kW · MW · hp · metric-hp · BTU/h · V · mV · kV · A · mA · kA · ohm · kohm · Mohm · mohm
to string yes
W · kW · MW · hp · metric-hp · BTU/h · V · mV · kV · A · mA · kA · ohm · kohm · Mohm · mohm

Example request

curl -X POST https://synsi.nl/api/v1/tools/electrical-units-converter \
  -H "Content-Type: application/json" \
  -d '{"value":10,"from":"V","to":"mV"}'

Example response

{
    "data": {
        "result": 10000
    },
    "meta": {
        "tool": "electrical-units-converter"
    }
}

Storage Calculator

Calculate how much storage a collection of files uses and how much capacity remains. Supports decimal GB and binary GiB units.

POST https://synsi.nl/api/v1/tools/storage-calculator

Parameters

Parameter Type Required Description
capacity number yes
capacity_unit string no
B · KB · MB · GB · TB · KiB · MiB · GiB · TiB
default: GB
file_size number yes
file_unit string no
B · KB · MB · GB · TB · KiB · MiB · GiB · TiB
default: GB
file_count integer yes

Example request

curl -X POST https://synsi.nl/api/v1/tools/storage-calculator \
  -H "Content-Type: application/json" \
  -d '{"capacity":512,"file_size":2,"file_count":100}'

Example response

{
    "data": {
        "capacity_bytes": 512000000000,
        "used_bytes": 200000000000,
        "available_bytes": 312000000000,
        "used_percent": 39.0625,
        "fits": true
    },
    "meta": {
        "tool": "storage-calculator"
    }
}

Download Time Calculator

Estimate download time from file size and internet speed. Convert GB, GiB and Mbps to a clear time estimate in seconds, minutes and hours.

POST https://synsi.nl/api/v1/tools/download-time-calculator

Parameters

Parameter Type Required Description
file_size number yes
file_unit string no
B · KB · MB · GB · TB · KiB · MiB · GiB · TiB
default: GB
connection_speed number yes
speed_unit string no
bit/s · Kbit/s · Mbit/s · Gbit/s · B/s · KB/s · MB/s · GB/s · KiB/s · MiB/s · GiB/s
default: Mbit/s

Example request

curl -X POST https://synsi.nl/api/v1/tools/download-time-calculator \
  -H "Content-Type: application/json" \
  -d '{"file_size":100,"connection_speed":100}'

Example response

{
    "data": {
        "seconds": 8000,
        "minutes": 133.333333333,
        "hours": 2.22222222222,
        "duration": "2h 13m 20s"
    },
    "meta": {
        "tool": "download-time-calculator"
    }
}

Discount Calculator

Calculate the savings and sale price after a percentage discount.

POST https://synsi.nl/api/v1/tools/discount-calculator

Parameters

Parameter Type Required Description
price number no
default: 100
discount_rate number no
default: 20
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/discount-calculator \
  -H "Content-Type: application/json" \
  -d '{"price":100,"discount_rate":20}'

Example response

{
    "data": {
        "discount_amount": 20,
        "sale_price": 80,
        "currency": "EUR"
    },
    "meta": {
        "tool": "discount-calculator"
    }
}

Investment Return Calculator

Compare an initial investment with its ending value and calculate total and annualized return.

POST https://synsi.nl/api/v1/tools/investment-return-calculator

Parameters

Parameter Type Required Description
initial_investment number no
default: 10000
final_value number no
default: 15000
years number no
default: 5
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/investment-return-calculator \
  -H "Content-Type: application/json" \
  -d '{"initial_investment":10000,"final_value":15000,"years":5}'

Example response

{
    "data": {
        "profit": 5000,
        "return_percent": 50,
        "annualized_return": 8.45,
        "currency": "EUR"
    },
    "meta": {
        "tool": "investment-return-calculator"
    }
}

ROI Calculator

Calculate net profit and return on investment from project cost and revenue.

POST https://synsi.nl/api/v1/tools/roi-calculator

Parameters

Parameter Type Required Description
investment_cost number no
default: 10000
revenue number no
default: 14000
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/roi-calculator \
  -H "Content-Type: application/json" \
  -d '{"investment_cost":10000,"revenue":14000}'

Example response

{
    "data": {
        "net_profit": 4000,
        "roi_percent": 40,
        "currency": "EUR"
    },
    "meta": {
        "tool": "roi-calculator"
    }
}

Tip Calculator

Work out a tip, the total bill and each person’s share.

POST https://synsi.nl/api/v1/tools/tip-calculator

Parameters

Parameter Type Required Description
bill number no
default: 80
tip_rate number no
default: 18
people integer no
default: 2
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/tip-calculator \
  -H "Content-Type: application/json" \
  -d '{"bill":80,"tip_rate":18,"people":2}'

Example response

{
    "data": {
        "tip_total": 14.4,
        "total_bill": 94.4,
        "per_person": 47.2,
        "tip_per_person": 7.2,
        "currency": "EUR"
    },
    "meta": {
        "tool": "tip-calculator"
    }
}

Split Bill Calculator

Add tax and tip to a bill, then split the total evenly across a group.

POST https://synsi.nl/api/v1/tools/split-bill-calculator

Parameters

Parameter Type Required Description
bill number no
default: 120
tax_rate number no
default: 0
tip_rate number no
default: 18
people integer no
default: 4
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/split-bill-calculator \
  -H "Content-Type: application/json" \
  -d '{"bill":120,"tax_rate":0,"tip_rate":18,"people":4}'

Example response

{
    "data": {
        "tax_total": 0,
        "tip_total": 21.6,
        "total_bill": 141.6,
        "per_person": 35.4,
        "currency": "EUR"
    },
    "meta": {
        "tool": "split-bill-calculator"
    }
}

Salary Calculator

Convert gross annual salary into an estimated gross and take-home amount per pay period.

POST https://synsi.nl/api/v1/tools/salary-calculator

Parameters

Parameter Type Required Description
annual_salary number no
default: 50000
deduction_rate number no
default: 25
pay_frequency string no
weekly · biweekly · monthly
default: monthly
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/salary-calculator \
  -H "Content-Type: application/json" \
  -d '{"annual_salary":50000,"deduction_rate":25}'

Example response

{
    "data": {
        "gross_per_period": 4166.67,
        "estimated_deduction": 1041.67,
        "net_per_period": 3125,
        "estimated_net_annual": 37500,
        "currency": "EUR"
    },
    "meta": {
        "tool": "salary-calculator"
    }
}

Hourly to Annual Salary Calculator

Convert an hourly wage to an annual estimate or an annual salary to an hourly equivalent.

POST https://synsi.nl/api/v1/tools/hourly-annual-salary-calculator

Parameters

Parameter Type Required Description
mode string no
hourly_to_annual · annual_to_hourly
default: hourly_to_annual
hourly_rate number no
default: 25
annual_salary number no
default: 52000
hours_per_week number no
default: 40
weeks_per_year number no
default: 52
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/hourly-annual-salary-calculator \
  -H "Content-Type: application/json" \
  -d '{"hourly_rate":25,"annual_salary":52000,"hours_per_week":40,"weeks_per_year":52}'

Example response

{
    "data": {
        "annual_salary": 52000,
        "hourly_rate": 25,
        "monthly_salary": 4333.33,
        "currency": "EUR"
    },
    "meta": {
        "tool": "hourly-annual-salary-calculator"
    }
}

Overtime Calculator

Estimate regular and overtime pay for a work period using your hourly rate and overtime multiplier.

POST https://synsi.nl/api/v1/tools/overtime-calculator

Parameters

Parameter Type Required Description
hourly_rate number no
default: 25
regular_hours number no
default: 40
overtime_hours number no
default: 5
multiplier number no
default: 1.5
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/overtime-calculator \
  -H "Content-Type: application/json" \
  -d '{"hourly_rate":25,"regular_hours":40,"overtime_hours":5,"multiplier":1.5}'

Example response

{
    "data": {
        "regular_pay": 1000,
        "overtime_pay": 187.5,
        "total_pay": 1187.5,
        "currency": "EUR"
    },
    "meta": {
        "tool": "overtime-calculator"
    }
}

Pay Raise Calculator

Calculate your new annual salary and the value of a percentage raise.

POST https://synsi.nl/api/v1/tools/pay-raise-calculator

Parameters

Parameter Type Required Description
current_salary number no
default: 50000
raise_rate number no
default: 5
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/pay-raise-calculator \
  -H "Content-Type: application/json" \
  -d '{"current_salary":50000,"raise_rate":5}'

Example response

{
    "data": {
        "raise_amount": 2500,
        "new_salary": 52500,
        "monthly_increase": 208.33,
        "currency": "EUR"
    },
    "meta": {
        "tool": "pay-raise-calculator"
    }
}

Rent vs Buy Calculator

Compare estimated rent payments with net homeownership costs over a selected time period.

POST https://synsi.nl/api/v1/tools/rent-vs-buy-calculator

Parameters

Parameter Type Required Description
home_price number no
default: 350000
down_payment_rate number no
default: 20
mortgage_rate number no
default: 4
mortgage_years integer no
default: 30
compare_years integer no
default: 10
monthly_rent number no
default: 1800
rent_increase_rate number no
default: 3
home_appreciation_rate number no
default: 3
property_tax_rate number no
default: 1
maintenance_rate number no
default: 1
insurance_annual number no
default: 1200
closing_cost_rate number no
default: 3
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/rent-vs-buy-calculator \
  -H "Content-Type: application/json" \
  -d '{"home_price":350000,"down_payment_rate":20,"mortgage_rate":4,"mortgage_years":30,"compare_years":10,"monthly_rent":1800,"rent_increase_rate":3,"home_appreciation_rate":3,"property_tax_rate":1,"maintenance_rate":1,"insurance_annual":1200,"closing_cost_rate":3}'

Example response

{
    "data": {
        "rent_cost": 247619.79,
        "buy_net_cost": 84681.17,
        "home_equity": 249775.65,
        "difference": 162938.62,
        "lower_cost": "buy",
        "currency": "EUR"
    },
    "meta": {
        "tool": "rent-vs-buy-calculator"
    }
}

Debt Payoff Calculator

Estimate payoff time and interest from a debt balance, APR and fixed monthly payment.

POST https://synsi.nl/api/v1/tools/debt-payoff-calculator

Parameters

Parameter Type Required Description
balance number no
default: 10000
apr number no
default: 18
monthly_payment number no
default: 500
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/debt-payoff-calculator \
  -H "Content-Type: application/json" \
  -d '{"balance":10000,"apr":18,"monthly_payment":500}'

Example response

{
    "data": {
        "will_pay_off": true,
        "months_to_payoff": 24,
        "total_interest": 1978.27,
        "total_paid": 11978.27,
        "currency": "EUR"
    },
    "meta": {
        "tool": "debt-payoff-calculator"
    }
}

Credit Card Interest Calculator

Estimate credit card interest and remaining balance over a selected number of months.

POST https://synsi.nl/api/v1/tools/credit-card-interest-calculator

Parameters

Parameter Type Required Description
balance number no
default: 3000
apr number no
default: 24
monthly_payment number no
default: 200
months integer no
default: 12
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/credit-card-interest-calculator \
  -H "Content-Type: application/json" \
  -d '{"balance":3000,"apr":24,"monthly_payment":200,"months":12}'

Example response

{
    "data": {
        "first_month_interest": 59.75,
        "interest_over_period": 519.79,
        "balance_after_period": 1119.79,
        "months_elapsed": 12,
        "currency": "EUR"
    },
    "meta": {
        "tool": "credit-card-interest-calculator"
    }
}

Emergency Fund Calculator

Set a savings target from monthly essential expenses and estimate how long to fill the gap.

POST https://synsi.nl/api/v1/tools/emergency-fund-calculator

Parameters

Parameter Type Required Description
monthly_expenses number no
default: 3000
months_target integer no
default: 6
current_savings number no
default: 1000
monthly_contribution number no
default: 300
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/emergency-fund-calculator \
  -H "Content-Type: application/json" \
  -d '{"monthly_expenses":3000,"months_target":6,"current_savings":1000,"monthly_contribution":300}'

Example response

{
    "data": {
        "target_fund": 18000,
        "remaining": 17000,
        "months_to_goal": 57,
        "currency": "EUR"
    },
    "meta": {
        "tool": "emergency-fund-calculator"
    }
}

Retirement Calculator

Project savings to a target retirement age and compare the result with an income-based target.

POST https://synsi.nl/api/v1/tools/retirement-calculator

Parameters

Parameter Type Required Description
current_age integer no
default: 35
retirement_age integer no
default: 67
current_savings number no
default: 25000
monthly_contribution number no
default: 500
annual_return number no
default: 5
desired_monthly_income number no
default: 3000
withdrawal_rate number no
default: 4
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/retirement-calculator \
  -H "Content-Type: application/json" \
  -d '{"current_age":35,"retirement_age":67,"current_savings":25000,"monthly_contribution":500,"annual_return":5,"desired_monthly_income":3000,"withdrawal_rate":4}'

Example response

{
    "data": {
        "projected_balance": 581178.9,
        "target_balance": 900000,
        "surplus_or_gap": -318821.1,
        "years_to_retirement": 32,
        "currency": "EUR"
    },
    "meta": {
        "tool": "retirement-calculator"
    }
}

Paint Calculator

Estimate wall area and the paint needed for one or more coats, including an allowance for paint lost to spills and touch-ups.

POST https://synsi.nl/api/v1/tools/paint-calculator

Parameters

Parameter Type Required Description
wall_length number no
default: 4
wall_height number no
default: 2.5
wall_count integer no
default: 4
openings_area number no
default: 4
coats integer no
default: 2
coverage number no
default: 10
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/paint-calculator \
  -H "Content-Type: application/json" \
  -d '{"wall_length":4,"wall_height":2.5,"wall_count":4,"openings_area":4,"coats":2,"coverage":10,"waste_percent":10}'

Example response

{
    "data": {
        "paint_liters": 7.92,
        "paint_gallons": 2.09,
        "wall_area": 36,
        "unit": "metric"
    },
    "meta": {
        "tool": "paint-calculator"
    }
}

Flooring Calculator

Estimate the floor area for one or more rooms, add a cutting-waste allowance and calculate how many flooring packs to buy.

POST https://synsi.nl/api/v1/tools/flooring-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 4
rooms integer no
default: 1
package_coverage number no
default: 2.2
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/flooring-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":4,"rooms":1,"package_coverage":2.2,"waste_percent":10}'

Example response

{
    "data": {
        "required_area": 22,
        "packages": 10,
        "leftover_area": 0,
        "unit": "metric"
    },
    "meta": {
        "tool": "flooring-calculator"
    }
}

Tile Calculator

Calculate the number of floor tiles and boxes needed from room size, tile dimensions, box quantity and a cutting-waste allowance.

POST https://synsi.nl/api/v1/tools/tile-calculator

Parameters

Parameter Type Required Description
length number no
default: 4
width number no
default: 3
tile_width number no
default: 30
tile_height number no
default: 30
tiles_per_box integer no
default: 10
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/tile-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":4,"width":3,"tile_width":30,"tile_height":30,"tiles_per_box":10,"waste_percent":10}'

Example response

{
    "data": {
        "tiles": 147,
        "boxes": 15,
        "tile_area": 12,
        "unit": "metric"
    },
    "meta": {
        "tool": "tile-calculator"
    }
}

Concrete Calculator

Estimate concrete volume and the number of ready-mix bags for a rectangular slab, footing or post base.

POST https://synsi.nl/api/v1/tools/concrete-calculator

Parameters

Parameter Type Required Description
length number no
default: 3
width number no
default: 2
depth number no
default: 10
bag_yield_liters number no
default: 25
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/concrete-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":3,"width":2,"depth":10,"bag_yield_liters":25,"waste_percent":10}'

Example response

{
    "data": {
        "volume_m3": 0.66,
        "volume_ft3": 23.31,
        "bags": 27
    },
    "meta": {
        "tool": "concrete-calculator"
    }
}

Gravel Calculator

Estimate the gravel volume for a rectangular area from its length, width and planned depth, with an optional extra allowance.

POST https://synsi.nl/api/v1/tools/gravel-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 3
depth number no
default: 5
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/gravel-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":3,"depth":5,"waste_percent":10}'

Example response

{
    "data": {
        "volume_m3": 0.83,
        "volume_ft3": 29.13,
        "volume_liters": 825,
        "unit": "metric"
    },
    "meta": {
        "tool": "gravel-calculator"
    }
}

Mulch Calculator

Work out the volume of mulch needed to cover a garden bed at your chosen depth, including an optional extra allowance.

POST https://synsi.nl/api/v1/tools/mulch-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 3
depth number no
default: 5
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/mulch-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":3,"depth":5,"waste_percent":10}'

Example response

{
    "data": {
        "volume_m3": 0.83,
        "volume_ft3": 29.13,
        "volume_liters": 825,
        "unit": "metric"
    },
    "meta": {
        "tool": "mulch-calculator"
    }
}

Soil Calculator

Estimate the amount of topsoil or garden soil needed to fill a rectangular bed or raised planter.

POST https://synsi.nl/api/v1/tools/soil-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 3
depth number no
default: 5
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/soil-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":3,"depth":5,"waste_percent":10}'

Example response

{
    "data": {
        "volume_m3": 0.83,
        "volume_ft3": 29.13,
        "volume_liters": 825,
        "unit": "metric"
    },
    "meta": {
        "tool": "soil-calculator"
    }
}

Wallpaper Calculator

Estimate wallpaper rolls from wall dimensions and roll size, with extra material for matching a repeating pattern.

POST https://synsi.nl/api/v1/tools/wallpaper-calculator

Parameters

Parameter Type Required Description
wall_width number no
default: 4
wall_height number no
default: 2.5
wall_count integer no
default: 4
roll_width number no
default: 0.53
roll_length number no
default: 10
pattern_waste_percent number no
default: 15
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/wallpaper-calculator \
  -H "Content-Type: application/json" \
  -d '{"wall_width":4,"wall_height":2.5,"wall_count":4,"roll_width":0.53,"roll_length":10,"pattern_waste_percent":15}'

Example response

{
    "data": {
        "rolls": 9,
        "wall_area": 40,
        "unit": "metric"
    },
    "meta": {
        "tool": "wallpaper-calculator"
    }
}

Roofing Calculator

Estimate roof covering area from roof length, sloped length, roof sections and a waste allowance.

POST https://synsi.nl/api/v1/tools/roofing-calculator

Parameters

Parameter Type Required Description
roof_length number no
default: 10
slope_length number no
default: 6
sections integer no
default: 2
waste_percent number no
default: 10
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/roofing-calculator \
  -H "Content-Type: application/json" \
  -d '{"roof_length":10,"slope_length":6,"sections":2,"waste_percent":10}'

Example response

{
    "data": {
        "roof_area": 132,
        "squares": 14.21,
        "unit": "metric"
    },
    "meta": {
        "tool": "roofing-calculator"
    }
}

BTU Heating Calculator

Estimate the heating output in watts and BTU per hour from room floor area and an adjustable heat-load assumption.

POST https://synsi.nl/api/v1/tools/btu-heating-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 4
watts_per_m2 number no
default: 100
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/btu-heating-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":4,"watts_per_m2":100}'

Example response

{
    "data": {
        "heat_watts": 2000,
        "heat_btu": 6824
    },
    "meta": {
        "tool": "btu-heating-calculator"
    }
}

Air Conditioner Size Calculator

Estimate a room air conditioner size in BTU per hour and cooling tons from room area, sun exposure and occupancy.

POST https://synsi.nl/api/v1/tools/ac-size-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 4
people integer no
default: 2
sunlight string no
shaded · average · sunny
default: average
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/ac-size-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":4,"people":2}'

Example response

{
    "data": {
        "cooling_btu": 6000,
        "cooling_tons": 0.5
    },
    "meta": {
        "tool": "ac-size-calculator"
    }
}

Electricity Cost Calculator

Estimate monthly energy use and electricity cost for an appliance from its wattage, daily use and your price per kilowatt-hour.

POST https://synsi.nl/api/v1/tools/electricity-cost-calculator

Parameters

Parameter Type Required Description
power_watts number no
default: 1000
hours_per_day number no
default: 5
days_per_month integer no
default: 30
rate_per_kwh number no
default: 0.3
currency string no
EUR · USD · GBP
default: EUR

Example request

curl -X POST https://synsi.nl/api/v1/tools/electricity-cost-calculator \
  -H "Content-Type: application/json" \
  -d '{"power_watts":1000,"hours_per_day":5,"days_per_month":30,"rate_per_kwh":0.3}'

Example response

{
    "data": {
        "monthly_kwh": 150,
        "monthly_cost": 45,
        "annual_cost": 540,
        "currency": "EUR"
    },
    "meta": {
        "tool": "electricity-cost-calculator"
    }
}

Solar Panel Calculator

Estimate a solar array size and panel count from monthly electricity use, peak sun hours, system efficiency and panel wattage.

POST https://synsi.nl/api/v1/tools/solar-panel-calculator

Parameters

Parameter Type Required Description
monthly_usage_kwh number no
default: 300
sun_hours number no
default: 4
system_efficiency number no
default: 80
panel_watts number no
default: 400

Example request

curl -X POST https://synsi.nl/api/v1/tools/solar-panel-calculator \
  -H "Content-Type: application/json" \
  -d '{"monthly_usage_kwh":300,"sun_hours":4,"system_efficiency":80,"panel_watts":400}'

Example response

{
    "data": {
        "system_kw": 3.13,
        "panels": 8,
        "annual_generation": 3738
    },
    "meta": {
        "tool": "solar-panel-calculator"
    }
}

Water Tank Calculator

Calculate the capacity of a rectangular or cylindrical water tank from its internal dimensions.

POST https://synsi.nl/api/v1/tools/water-tank-calculator

Parameters

Parameter Type Required Description
shape string no
rectangular · cylindrical
default: rectangular
length number no
default: 2
width number no
default: 1
diameter number no
default: 1
height number no
default: 1.5
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/water-tank-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":2,"width":1,"diameter":1,"height":1.5}'

Example response

{
    "data": {
        "capacity_liters": 3000,
        "capacity_gallons": 793
    },
    "meta": {
        "tool": "water-tank-calculator"
    }
}

Room Area Calculator

Calculate the floor area and combined perimeter for one or more rectangular rooms in metric or imperial units.

POST https://synsi.nl/api/v1/tools/room-area-calculator

Parameters

Parameter Type Required Description
length number no
default: 5
width number no
default: 4
rooms integer no
default: 1
unit string no
metric · imperial
default: metric

Example request

curl -X POST https://synsi.nl/api/v1/tools/room-area-calculator \
  -H "Content-Type: application/json" \
  -d '{"length":5,"width":4,"rooms":1}'

Example response

{
    "data": {
        "area_m2": 20,
        "area_ft2": 215.28,
        "perimeter": 18,
        "unit": "metric"
    },
    "meta": {
        "tool": "room-area-calculator"
    }
}

Sudoku

Play Sudoku free in your browser: four difficulty levels, notes, hints, undo and a timer. Every puzzle has exactly one solution. Share a puzzle with a link. No sign-up, no ads.

POST https://synsi.nl/api/v1/tools/sudoku

Parameters

Parameter Type Required Description
mode string no generate a new puzzle, or solve the given one.
generate · solve
default: generate
difficulty string no Difficulty of a generated puzzle (given cells: easy 40, medium 33, hard 28, expert about 24).
easy · medium · hard · expert
default: medium
seed integer no Optional: the same seed and difficulty always give the same puzzle (e.g. 20261015). Random when left out.
puzzle string no For solve: 81 cells row by row, digits with 0 or "." for empty cells; spaces and line breaks are ignored.

Example request

curl -X POST https://synsi.nl/api/v1/tools/sudoku \
  -H "Content-Type: application/json" \
  -d '{"puzzle":"530070000600195000098000060800060003400803001700020006060000280000419005000080079"}'

Example response

{
    "data": {
        "difficulty": "medium",
        "seed": 2126417682,
        "puzzle": "685010000010070308040090602108000004000109000097006580502030090830060100000700820",
        "solution": "685213749219674358743598612128357964456189237397426581572831496834962175961745823",
        "givens": 33
    },
    "meta": {
        "tool": "sudoku"
    }
}