caldays vs Non-Working Days

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.

isdayoff.ru answers one narrow question extremely cheaply: for a date or date range, is it a working day, a weekend, or an official non-working holiday. Responses are bare digit strings (0/1 per day, or 2 for a shortened day) rather than JSON, which keeps payloads tiny for the batch/range endpoint. It documents Russia, Belarus, Ukraine, Kazakhstan, and the US as supported country codes, but live probes this run found only Russia (the default), Belarus, and Kazakhstan return genuinely varying data — the Ukraine and US codes are accepted (HTTP 200) but answered every single day of several different months with a flat, undifferentiated "0". It's free, keyless, and has no published rate limit, built for production-calendar bookkeeping rather than general holiday metadata.