
Check if a date is a Russian holiday or not.
Russian Calendar API is a free Calendar API that requires no API key, is served over HTTPS and does not support CORS, so it should be called from a server.
Work calendar service.
Details from github.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.
Public holidays for US states and 30 countries plus sports and finance calendars as static JSON
Simple REST API for checking working, non-working or short days for Russia, CIS, USA and other
Provides namedays for multiple countries
The Russian Calendar API is provided by egno (github.com). Work calendar service.
Yes. The Russian Calendar 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.
No. The Russian Calendar API requires no authentication, so you can start making requests without signing up.
Not directly. The Russian Calendar API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The Russian Calendar API is served over HTTPS, so it's safe to use in production.