Weather and forecast data from Spain.
Aemet API is a free Weather API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.

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Yes. The Aemet API is listed in the Weather 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 Aemet API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Aemet API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Aemet API is served over HTTPS, so it's safe to use in production.