Manage DNS, CDN, Workers and other services; documented with an official OpenAPI 3.0 spec.
Cloudflare API is a free Development API that requires apiKey authentication, is served over HTTPS and does not support CORS, so it should be called from a server.
Details from developers.cloudflare.com.

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The Cloudflare API is provided by Cloudflare API (developers.cloudflare.com).
Yes. The Cloudflare 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 Cloudflare API uses apiKey authentication, so you need to register for credentials before making requests.
Not directly. The Cloudflare API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The Cloudflare API is served over HTTPS, so it's safe to use in production.