Easter & Computus API
Computus and calendar maths as an API, computed locally and deterministically. The easter endpoint computes the date of Easter Sunday for any year — both the Western date, by the Anonymous Gregorian (Meeus/Jones/Butcher) algorithm, and the Orthodox date, by the Julian computus converted to the Gregorian calendar — with the month name and weekday; Easter is the first Sunday after the paschal full moon, so 2024 falls on 31 March in the West and 5 May for the Orthodox church, while in 2025 both coincide on 20 April. The movable-feasts endpoint returns the whole Easter-anchored cycle for a year as calendar dates — Ash Wednesday (−46 days), Palm Sunday (−7), Maundy Thursday (−3), Good Friday (−2), Ascension (+39), Pentecost (+49) and Corpus Christi (+60). The julian-day endpoint converts a Gregorian date to its Julian Day Number — the continuous day count astronomers use, where 2451545 is 1 January 2000 — and back, returning the weekday too. Years are in the Gregorian calendar. Everything is computed locally and deterministically, so it is instant and private. Ideal for calendar, scheduling, liturgical, church, holiday-planning and date-arithmetic app developers, movable-feast and Julian-day tools, and almanac software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is the computus and Julian-day conversion; for general date arithmetic and time zones use a date-time API.
api.oanor.com/easter-api
