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Metadata for all families served by Google Fonts.
Google Fonts API is a free Development API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Details from developers.google.com.

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