# Calendar Systems

Date conversion and calendar facts for agents: Julian Day, Julian, Hebrew, Islamic tabular and Persian calendars, Chinese zodiac, moon phases and seasons.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://calendar-systems.x402tookit.com/openapi.json
- x402 manifest: https://calendar-systems.x402tookit.com/.well-known/x402
- Catalog (free): https://calendar-systems.x402tookit.com/catalog
- Health (free): https://calendar-systems.x402tookit.com/health
- Uptime (free): https://calendar-systems.x402tookit.com/uptime

## Endpoints (12)

### GET /age-profile — $0.02
Age in years, months, days and days lived, Korean and East Asian ages, next birthday with leap-day rules, and zodiac.
Params: birth: string, asOf?: string
Example: https://calendar-systems.x402tookit.com/age-profile?birth=1992-02-29&asOf=2026-10-11

### GET /chinese-zodiac — $0.02
Chinese zodiac animal, element, yin/yang and Chinese New Year date for a year or a date (New Year table 1901-2100).
Params: year?: integer, date?: string
Example: https://calendar-systems.x402tookit.com/chinese-zodiac?date=2024-01-15

### GET /day-of-week — $0.02
Weekday of any date from year 1 to 9999 (Gregorian or Julian calendar) with day of year, quarter, ISO week and ISO week-date.
Params: date?: string, calendar?: string, isoWeek?: string
Example: https://calendar-systems.x402tookit.com/day-of-week?date=2026-10-11

### GET /hebrew-calendar — $0.02
Convert a Gregorian date to the Hebrew calendar (or back) with leap year, year type and major holiday dates.
Params: date: string, from?: string
Example: https://calendar-systems.x402tookit.com/hebrew-calendar?date=2024-10-03

### GET /islamic-calendar — $0.02
Convert a Gregorian date to the Islamic tabular civil calendar (or back); a calculated approximation, not moon sighting.
Params: date: string, from?: string
Example: https://calendar-systems.x402tookit.com/islamic-calendar?date=2024-03-11

### GET /julian-calendar — $0.02
Convert between Gregorian and Julian calendar dates (Old Style / New Style) with the day difference for that date.
Params: date: string, from?: string
Example: https://calendar-systems.x402tookit.com/julian-calendar?date=2025-01-07

### GET /julian-day — $0.02
Julian Day, modified JD and Julian Day Number for a date and UTC time (Gregorian or Julian calendar), or JD back to a date.
Params: date?: string, time?: string, calendar?: string, jd?: number
Example: https://calendar-systems.x402tookit.com/julian-day?date=1957-10-04&time=19%3A26%3A24

### GET /leap-year — $0.02
Is a year a leap year in the Gregorian, Julian, Hebrew, Islamic (tabular) or Persian calendar? Rule and nearby leap years.
Params: year: integer, calendar?: string
Example: https://calendar-systems.x402tookit.com/leap-year?year=1900&calendar=gregorian

### GET /moon-calendar — $0.02
All new moons, first quarters, full moons and last quarters in a month (UTC) with times and a blue-moon flag.
Params: month: string
Example: https://calendar-systems.x402tookit.com/moon-calendar?month=2026-05

### GET /moon-phase — $0.02
Moon phase name, age in days, approximate illumination and the previous/next new, quarter and full moon times for a date.
Params: date: string, time?: string
Example: https://calendar-systems.x402tookit.com/moon-phase?date=2024-04-08&time=19%3A00

### GET /persian-calendar — $0.02
Convert a Gregorian date to the Persian Solar Hijri calendar (or back) using the astronomical Nowruz rule, 1901-2100.
Params: date: string, from?: string
Example: https://calendar-systems.x402tookit.com/persian-calendar?date=2025-03-21

### GET /seasons — $0.02
March and September equinox and June and December solstice moments (UTC) for a year, with season lengths in days.
Params: year: integer
Example: https://calendar-systems.x402tookit.com/seasons?year=2026

## Terms

Results are computed locally from published calendar and astronomy algorithms, provided as is, with no warranty. Islamic dates are the tabular approximation and may differ from observed month starts by a day or two; religious observance dates must be confirmed with the relevant authority. Astronomical times carry the stated accuracy only.