API Tester
Test REST API endpoints with custom methods, headers, and request bodies. View formatted responses instantly.
Request
Introduction
Every developer who builds or integrates with web APIs needs a fast way to send requests and inspect responses without writing throwaway scripts or booting up a heavy desktop application. Whether you are verifying that a new endpoint returns the expected status code, debugging why a webhook is rejecting your payload, or checking response headers for caching directives, an in-browser API tester lets you iterate on requests in seconds rather than minutes.
What Is API Tester?
API Tester is a browser-based HTTP client that lets you construct and send requests to any REST, GraphQL, or webhook endpoint directly from your browser tab. You set the method (GET, POST, PUT, PATCH, DELETE, OPTIONS), enter the URL, add headers, query parameters, and a request body — then hit send and see the full response: status code, response time, headers, and body in both raw and formatted views. It handles JSON and form-urlencoded bodies natively, with automatic Content-Type header management.
The tool is designed around the real workflows of API development. You can save a collection of requests and re-run them after a deployment to confirm nothing broke. You can inspect the exact bytes coming back from the server — useful when a backend team claims they fixed a CORS issue but the preflight response still lacks the Access-Control-Allow-Headers entry. Response times are measured to the millisecond, making it easy to spot endpoints that have regressed from 120ms to 2.4 seconds between releases.
Requests execute from your browser using the Fetch API, so your authentication tokens, API keys, and session cookies stay on your device. There is no proxy server logging your traffic, and no third-party backend that could leak your staging credentials. The only network hop is between your machine and the target API.
API Tester Examples
| Input | Output |
|---|---|
| GET https://api.github.com/repos/facebook/react with header Accept: application/vnd.github.v3+json | 200 OK — 340ms, response body includes stargazers_count: 225000, license: "MIT", default_branch: "main" |
| POST https://api.example.com/orders with JSON body {"item":"widget","qty":5} and Bearer token auth | 201 Created — 187ms, Location header points to /orders/8342, response includes order_id and estimated_delivery |
| OPTIONS https://api.cross-origin.dev/data (preflight check) | 204 No Content — Access-Control-Allow-Origin: https://yourapp.dev, Allow-Methods: GET, POST, Allow-Headers: Authorization, Content-Type |
Key Features of API Tester
- Full HTTP method support including PATCH, OPTIONS, and custom methods for non-standard APIs
- Automatic JSON formatting and syntax highlighting for response bodies
- Request history that stores your last 50 requests with full headers and payloads for quick re-execution
- Bearer token and Basic auth headers generated from a single credentials input field
- Response time measurement accurate to the millisecond with size reporting in bytes
- Header inspection for both request and response, including Set-Cookie and CORS preflight headers
- Request collection save-and-reload so you can build a regression test suite for your own APIs
How It Works
Configure Your HTTP Request
Set the HTTP method (GET, POST, PUT, PATCH, or DELETE), enter the endpoint URL, and add any request headers, query parameters, or body payload. You can paste a JSON body directly into the editor or use the form-data editor for multipart requests.
Send and Inspect the Full Response
Hit send and the tool makes the request from your browser, then displays the status code, response headers, and body in separate tabs. JSON responses are automatically formatted with syntax highlighting, and timing information shows how long each phase of the request took.
Iterate on Your Request
Modify request headers, adjust the request payload, or change the HTTP method and re-send without losing any of your previous configuration. The response area updates with each new request so you can compare results across different inputs, parameters, or authentication tokens.
Who Uses This
Backend Developers
testing new API endpoints during development and verifying response shapes, status codes, and error messages before writing frontend integration code
Integration Engineers
debugging third-party API integrations by sending test requests with different authentication headers and payload variations to isolate connection or permission issues
Mobile Developers
validating API behavior from a desktop browser before implementing the same calls in their mobile app, saving build-and-deploy cycles during early integration work