
Pictures of cats from Tumblr.
Cats API is a free Animals API that requires apiKey authentication, is served over HTTPS and does not support CORS, so it should be called from a server.
Open API for cat images and breeds
Details from docs.thecatapi.com.

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The Cats API is provided by The Cat API (docs.thecatapi.com). Open API for cat images and breeds
Yes. The Cats API is listed in the Animals 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 Cats API uses apiKey authentication, so you need to register for credentials before making requests.
Not directly. The Cats API does not allow CORS, so call it from a server, serverless function or proxy instead of front-end JavaScript.
Yes. The Cats API is served over HTTPS, so it's safe to use in production.