Documentation

This service answers one GET request at a time, in plain text, without a key: exact computations, reference data copied from primary publishers, and facts about your own connection. These pages are for people, and for anyone arriving from a search, who want to know what an endpoint does before calling it.

Each group of endpoints has a page listing every path with its parameters and an example. Some topics also have a page of their own, because the obvious way of solving them produces an answer that looks right and is not; those pages explain the mistake first and the endpoint second.

Machine clients will find the same information in a form easier to parse at /agents.md, /llms.txt and /openapi.json.

Time and dates

Current time, parsing, conversion, arithmetic, business days, cron, ISO weeks.

• Convert time between timezones: Convert a local time between IANA timezones. Times that never happen, or happen twice, when clocks change are refused with a reason instead of guessed.

Arithmetic and number theory

Arbitrary precision, exact fractions, expressions, statistics, number theory, loans.

Unit conversion

Length, mass, volume, temperature, pressure, energy, power, data, speed, area.

Identifier checks

IBAN, ISBN, EAN, Luhn, VIN, UUID, ISIN, LEI, phone numbers, national identifiers.

• Validate an IBAN: Check an IBAN's length and mod-97 check digits for its country. A valid result means the IBAN is well formed, not that the account exists or can receive money.

Encoding, hashing and tokens

base64/32/58, hex, URL, punycode, hashes, HMAC.

• Decode a JWT: Decode a JSON Web Token's header and payload in one request. Decoding shows what a token claims; it cannot show whether the claim is true or the token genuine.

Data formats

JSON, YAML, TOML, CSV validation and conversion, JSONPath, JSON Schema, diff, regex.

Unicode text

Unicode normalisation, codepoints, invisible and confusable characters, transliteration.

Networks, URLs and domains

CIDR arithmetic, IP classification, URL parsing, registrable domain, user agents.

Random values

UUID v4 and v7, integers, choices, passwords, bytes (CSPRNG, never cached).

Coordinates and distances

Great-circle distance, bearing, destination, coordinate formats, geohash, UTM, MGRS.

Sun, moon and satellites

Sunrise, sunset, twilight, moon phase, equinoxes, satellite positions - computed, not looked up.

• Sunrise and sunset times: Sunrise, sunset and twilight for any place and date, in the timezone you name. Why a UTC sunset at 00:30 is correct and still reads like broken data.

Currency exchange rates from central banks

Currency reference rates (ECB) and official rates (Bank of Russia).

Public holidays by country

Public holidays and business days by country.

Reference tables

Country, currency, language, timezone, TLD, port, media type, HTTP and constant tables.

Earthquakes and space weather

Earthquakes, space weather.

Your own connection

Your request, your egress address, your client's capabilities.

Controlled responses for testing clients

Controlled responses for exercising your client.