AdoptAPet vs Cataas

AdoptAPet's free Pet List API lets a registered shelter or rescue pull its own current adoptable-pet listings — name, photo, breed, and a link back to the pet's page — for display on its own website; it doesn't cover other shelters' animals or expose network-wide search. Access needs a per-shelter API key passed as a key query parameter to endpoints like api.adoptapet.com/search/pets_at_shelter, confirmed live by a real GET that returns a JSON invalid_key error rather than a redirect or outage, with a separate OPTIONS preflight and that same GET both echoing access-control-allow-origin: * back for a test Origin header. The official documentation page now sits behind a shelter-account login (a live probe returns 401 with a Basic-auth challenge, a change from when it was openly readable), but the API endpoint itself remains fully live and free, returning JSON or XML depending on the output parameter.

Cataas ("Cat as a Service") is a free, open-source REST API that returns random cat images and animated GIFs, filterable by tag, with options to overlay custom text or crop a specific position. A JSON mode (?json=true) returns the image's metadata — id, tags, and direct URL — instead of the binary file itself. It's maintained on GitHub under the cataas org with no signup or pricing tier; a Donate link is the site's only monetization.