Free API Testing Tools
Working against an API means answering the same handful of questions over and over: what did the server actually return, what does this status code mean, what exactly goes in the Authorization header, and which Content-Type does this endpoint expect. These tools cover each of those without opening a heavyweight client or writing a throwaway script.
One honest caveat on the request tester specifically. It runs in your browser, so the browser's cross-origin rules apply: an API can only be called from this page if it sends an Access-Control-Allow-Origin header permitting it, and most public APIs do not. That is a limitation of every in-page API client, which is why desktop apps and proxies exist. The reference tools alongside it — status codes, headers, MIME types — have no such constraint and work entirely offline.
All API Testing Tools (4)
API Request Tester
Compose and send GET, POST, PUT, PATCH and DELETE requests with custom headers and a JSON body, then inspect the status, timing and response.
Launch ToolHTTP Status Code Lookup
Look up any HTTP status code and get what it means, when to use it, and which RFC defines it. Searchable reference covering 1xx through 5xx. Free and instant.
Launch ToolAuthorization Header Generator
Build a ready-to-paste Authorization header: Basic auth base64-encoded from a username and password, or a Bearer token. Free, instant, client-side.
Launch ToolMIME Type Lookup
Find the correct Content-Type for any file extension, with the gotchas that break uploads — image/jpeg for .jpg, image/svg+xml for .svg. Free and searchable.
Launch ToolFrequently Asked Questions
- Why does my request fail with a CORS error here but work in curl?
- Because curl is not a browser and does not enforce the same-origin policy. A browser will only let a page read a cross-origin response if the server opts in with an Access-Control-Allow-Origin header; curl has no such restriction and shows you the response regardless. The endpoint is fine — it just has not granted browsers from other origins permission to call it.
- Is the Authorization header generator safe to paste real credentials into?
- The encoding happens entirely in your browser and nothing is sent anywhere, so the generator itself is safe. The caution is about Basic auth itself: base64 is reversible in one step, so the header is only protected by HTTPS in transit, never by the encoding. The API Request Tester is different — it genuinely sends what you give it to the URL you enter.