Worldwide Holidays.
Calendarific API is a free Calendar API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Explore comprehensive holiday data worldwide with Calendarific. Access national holidays, local observances, and religious events with customizable API solutions for your needs.
Details from calendarific.com.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Industry-leading holiday data with over 5,000 holidays and thousands of descriptions
Public holidays and business days for all 54 African countries, from official sources
Catholic liturgical calendar
Lookup for a name and returns nameday date
The Calendarific API is provided by Calendarific (calendarific.com). Explore comprehensive holiday data worldwide with Calendarific. Access national holidays, local observances, and religious events with customizable API solutions for your needs.
Yes. The Calendarific API is listed in the Calendar category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Calendarific API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Calendarific API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Calendarific API is served over HTTPS, so it's safe to use in production.