caldays vs Church Calendar

Caldays provides free public holiday data for 206 countries in JSON format, plus long-weekend calculations and a world clock endpoint. Anonymous use is capped at 10,000 requests per day; a metered API key raises the limit for higher-volume needs. The holiday data carries a CC BY 4.0 licence, so users must credit Caldays in their app.

Church Calendar (calapi) serves the daily Roman Catholic liturgical calendar — season, week, feast rank, and liturgical color — for a given date and country-specific calendar variant, in English, Czech, Latin, or Spanish. It's a small keyless JSON API maintained by a Czech developer alongside the printed liturgical calendars he publishes. There's no pricing or account system of any kind; the only quirk is that its real backend still only serves plain HTTP, timing out on HTTPS.