Holiday data: OpenHolidays API (STUEBER SYSTEMS GmbH and contributors)
https://www.openholidaysapi.org/
Source documentation: https://www.openholidaysapi.org/en/sources-europe/
License: Open Database License (ODbL) 1.0
https://opendatacommons.org/licenses/odbl/1-0/

The JSON files contain unmodified records fetched from the public API,
grouped by country and year with retrieval metadata. They are downloadable
copies under the same ODbL license. Additional up-to-date records are
available via /api/holidays.php?country=CH&year=2026 (supported countries
CH, DE, AT, FR, ES, IT, PT; years 2020-2030).
No visitor data is included. Date ranges are inclusive. Coverage varies by
country, region, school type and year. Empty results do not establish that
no holiday exists. Consult the source authority for binding dates.