Fake REST API for testing and prototyping.
JSONPlaceholder API is a free Development API that requires no API key, is served over HTTPS and supports CORS, so it can be called from the browser.
Free fake and reliable API for testing and prototyping. Six resources, all HTTP methods, no signup.
Details from jsonplaceholder.typicode.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Convert JSON to JSONP (on-the-fly) for easy cross-domain data requests using client-side JavaScript
Simple key-value storage REST API for quick prototyping
Yes. The JSONPlaceholder 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.
No. The JSONPlaceholder API requires no authentication, so you can start making requests without signing up.
Yes. The JSONPlaceholder API supports CORS, so front-end JavaScript can call it directly.
Yes. The JSONPlaceholder API is served over HTTPS, so it's safe to use in production.