What is the API Response Tester?

It is a browser-based tool that lets you send HTTP requests (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS) to any URL and inspect the response including status code, headers, body, timing, and size.

Why do some requests fail with CORS errors?

Browser security policies prevent requests to servers that do not include CORS headers (Access-Control-Allow-Origin). This is a browser limitation, not a bug in the tool. Use APIs that support CORS or test with a local proxy.

Yes — completely free. Requests are sent directly from your browser using the Fetch API.

Can I send POST requests with a JSON body?

Yes. Select POST, PUT, or PATCH as the method, enter your JSON payload in the Body tab, and ensure the Content-Type header is set to application/json. The tool validates your JSON before sending.

Does it support authentication?

Yes. The Auth tab supports Basic Auth (username/password) and Bearer Token authentication. Credentials are added to the Authorization header automatically.

Can I generate a cURL command?

Yes. After sending a request, switch to the cURL tab in the response section to see the equivalent cURL command. You can copy it with one click.

Yes. Requests go directly from your browser to the target server. No data passes through ToolRux servers. However, the target API will receive your request data.

Can I cancel a request?

Yes. While a request is in progress, a Cancel button appears. You can also set a timeout (5s to 120s) to automatically abort slow requests.

API Response Tester

Send HTTP requests from your browser and inspect responses with status codes, headers, body, timing, authentication, and cURL export.

Note: Browser requests are subject to CORS policies. If the target API does not send Access-Control-Allow-Origin headers, the request will fail. This tool works best with CORS-enabled APIs and public endpoints.

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Everything you need to know

Browser-Based API Testing

Test any HTTP API directly from your browser without installing Postman, Insomnia, or curl. Send GET, POST, PUT, DELETE, PATCH, HEAD, and OPTIONS requests with custom headers, query parameters, authentication, and JSON request bodies. The tool displays the full response including the HTTP status code, response headers, formatted JSON body, response size, and request timing in milliseconds.

Query Parameters Builder

Build query strings visually with the Params tab. Add, remove, and toggle individual parameters on or off without manually editing the URL. Parameters are automatically URL-encoded and appended to your request URL. This is especially useful for APIs with many query parameters or complex filter expressions.

Custom Headers and Presets

Add any number of custom HTTP headers as key-value pairs. Use the preset menu to quickly add common headers like Content-Type, Accept, Cache-Control, and User-Agent. Each header can be individually enabled or disabled with a checkbox, making it easy to test different header combinations without deleting them.

Authentication Support

The Auth tab supports two common authentication methods. Basic Auth encodes your username and password into a Base64 Authorization header. Bearer Token adds your token (JWT, OAuth, API key) as a Bearer Authorization header. Credentials are applied automatically — no need to manually construct Authorization headers.

JSON Body Validation

For POST, PUT, and PATCH requests, enter a JSON request body in the Body tab. The tool validates your JSON syntax before sending and highlights errors with specific messages, so you catch typos, missing commas, and mismatched brackets before they hit the server.

Request Cancellation and Timeouts

Cancel in-flight requests at any time with the Cancel button. Set a request timeout (5s to 120s) to automatically abort slow requests that hang. This prevents the browser from waiting indefinitely for unresponsive servers and gives you immediate feedback.

Response Inspection

The response section shows the HTTP status code with color coding (green for 2xx, amber for 3xx, red for 4xx/5xx), response time, and response body size. JSON responses are automatically formatted with proper indentation and can be toggled between Pretty and Raw views. Switch between Body, Headers, and cURL tabs to inspect different aspects of the response.

cURL Command Generation

Every request you build can be exported as an equivalent cURL command. The cURL tab shows the full command with method, URL, headers, authentication, and body — ready to copy and paste into your terminal. This makes it easy to share requests with teammates or reproduce them in scripts.

Request History

The tool keeps a running history of your recent requests during the current session. Click any history entry to reload that method and URL. Each entry shows the HTTP method, URL, status code, and response time, making it easy to re-run previous requests or compare responses.

Download Response

Download the response body as a file with the appropriate extension (.json, .xml, .html, or .txt) based on the Content-Type header. This is useful for saving API responses for documentation, testing, or offline analysis.

CORS Limitations

Because this tool runs in the browser, requests are subject to Cross-Origin Resource Sharing (CORS) policies. APIs that do not include CORS headers will block browser requests. Most public APIs and JSONPlaceholder-style test APIs support CORS. For internal APIs, consider using a CORS proxy or a desktop HTTP client.

Privacy and Security

All requests are sent directly from your browser — no data passes through ToolRux servers. Authentication credentials, request bodies, and responses stay on your machine. However, be aware that the target API server will receive your request data including any credentials you include.

Related Developer Tools

Format JSON responses with the JSON Formatter, encode URLs with the URL Encoder, test CORS configurations with the CORS Tester, or generate CSP headers with the CSP Generator.