Test REST APIs directly from your browser — like Postman, but online
Headers
API Tester is a browser-based REST client that lets you fire HTTP requests and inspect the responses without installing Postman or Insomnia. Choose a method (GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS), enter a URL, attach custom headers, and send a raw JSON, form, or text body — then read back the status code, response headers, timing, and a formatted body all in one view.
It's built for backend and frontend developers, QA engineers, and anyone integrating with a third-party API who needs to confirm an endpoint behaves as expected. Because everything runs in your browser, it's handy for quick smoke tests, debugging auth headers like Bearer tokens, and verifying JSON payloads before wiring them into code.
The tool assembles a standard HTTP request from your inputs — method, URL, headers, and body — and dispatches it using the browser's fetch API. The response is parsed so you can see the status line, all returned headers, and the body pretty-printed when it is JSON. A round-trip timer reports roughly how long the server took to respond.
Because requests originate from your browser, they are subject to the same CORS (Cross-Origin Resource Sharing) rules the browser enforces for any web page. An API that does not send an Access-Control-Allow-Origin header for this site may block the request or hide the response body, even though the same call would succeed from a server or a desktop tool like curl. This is a browser security feature, not a bug in the endpoint.
A typical authenticated JSON request looks like: method POST, URL https://api.example.com/v1/orders, header Authorization: Bearer eyJhbGciOi..., header Content-Type: application/json, and a body such as {"item":"widget","qty":3}. The server would reply with a status like 201 Created and a JSON body echoing the created resource.
Yes, it is completely free with no sign-up. Requests are sent directly from your browser to the target API, and the URLs, headers, tokens, and bodies you enter are not stored on our servers.
Browsers enforce CORS on requests made from web pages, so an API must return an Access-Control-Allow-Origin header permitting this site. Command-line tools like curl and desktop apps like Postman are not bound by CORS, which is why the same request can succeed there.
The common REST methods are supported: GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS. Choose the one your endpoint expects for the operation you are performing.
Add an Authorization header with your credential, most often Authorization: Bearer <your-token> for token-based auth or Basic <base64> for basic auth. You can add any other custom headers your API requires the same way.
Set the method to POST, PUT, or PATCH, add a Content-Type: application/json header, and paste your JSON object into the body field. Make sure the JSON is valid, since malformed JSON will cause the server to reject the request.
This usually happens when the response is blocked by CORS, when the endpoint returns a non-text format like a binary file, or when the server responds with a status such as 204 No Content that has no body by design.
It depends on your setup. The browser must be able to reach the address, so localhost works if the API runs on your own machine, but private or internal hosts unreachable from your browser, or those missing CORS headers, may fail.