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About this tool
Build, send, and test API requests with ease.
API Tester is a browser-based REST client that builds and sends a request across all seven HTTP methods — GET, POST, PUT, PATCH, DELETE, HEAD and OPTIONS — then shows the status code, round-trip time in milliseconds, response size and full response headers. It supports query params, custom headers, a raw JSON body, Bearer and Basic auth, and {{variable}} placeholders that are substituted into the URL, headers and body before sending. Requests go straight from your browser to the target API, and saved collections, environment variables and the last 50 requests are kept in local storage on your own machine.
Open API TESTER on AltFTool — it loads instantly in your browser.
Type the endpoint into the URL bar — it accepts {{variables}} — or load one of the sample requests in the top bar (Get a post, List users, Create post, Random dog).
Pick the method (GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS), then fill the Params, Headers, Auth and Body tabs. Params are appended to the URL automatically, Auth offers No Auth, Bearer Token or Basic Auth, and Beautify JSON reformats the raw body.
Press Send (or Enter in the URL bar) and read the response: status code, time in ms and payload size, with Body and Headers tabs, a Pretty toggle for JSON, a copy button and a download button that saves response.json or response.txt. Cancel aborts an in-flight request, the Save icon files it under a collection, and the History tab keeps your last 50 sends.
Saved requests, environment variables and the 50 most recent calls stay in your browser's local storage between sessions — no account, no sync.
{{name}} placeholders are expanded in the URL, every header value and the request body at send time, so one change switches environments.
Every send reports status and status text, elapsed milliseconds, payload size in B/KB/MB, and the complete response header list, with JSON pretty-printing toggleable.
Almost always CORS. The request is made by your browser with fetch(), so the target API must return permissive Access-Control-Allow-Origin headers; desktop clients like Postman are not bound by that rule. There is no AltFTool proxy in between: credentials bypass AltFTool and travel directly from your browser to the target API you entered.
No. If the method is not GET or HEAD, the body is non-empty and you have not set a Content-Type header yourself, the tool adds Content-Type: application/json automatically. Set the header explicitly if you are sending form-encoded or plain-text bodies.
The 50 most recent requests are kept, newest first, in your browser's local storage along with saved collections and environment variables. AltFTool does not receive or sync that saved history; request details are transmitted to the target API when you send them. Clearing site data or using the Clear history button removes the local copy permanently.
Choosing Basic Auth and filling in a username and password sends an Authorization: Basic header whose value is the base64 encoding of username:password. Bearer Token mode sends Authorization: Bearer followed by your token, after any {{variables}} in it are substituted.