Free Calendar APIs

Church Calendar (calapi.inadiutorium.cz) is a free, no-auth REST API that returns the Roman Catholic liturgical calendar for any date or month.

The Czech Namedays Calendar API lets you look up the Czech or Slovak nameday (svátek) associated with a given first name, or find whose nameday falls on a specific date.

The Hebcal API provides free Jewish calendar data including Hebrew date conversions, Shabbat candle-lighting times, Jewish holidays, and weekly Torah portion readings.

LectServe is a free REST API that returns Revised Common Lectionary readings — Scripture passages assigned to each Sunday and feast day used by many Protestant denominations.

Nager.Date is a completely free, open-source REST API providing public holidays for over 90 countries with no API key required.

Namedays Calendar provides name day traditions for dozens of countries, letting you look up which names are celebrated on any given date.

Non-Working Days provides ICS calendar files for public holidays and non-working days across many countries, hosted as a structured database on GitHub.

IsDayOff.ru is a minimalist REST API that returns whether a given date is a working day, non-working day, or short (pre-holiday) day for Russia and several CIS countries, as well as the United States.

Russian Calendar API checks whether a specific date is a holiday, working day, or short day in Russia, based on official government decree data.

The UK Bank Holidays API is an official UK government endpoint that returns all bank holidays for England and Wales, Scotland, and Northern Ireland as structured JSON.