API Tester

API Tester is a free, browser-based tool for testing REST API endpoints instantly. Send HTTP requests with custom methods, headers, authentication, and request bodies — then inspect the response status, timing, headers, and formatted body. No installation or sign-up required. All requests are sent directly from your browser, keeping your data private.

What Is an API Tester?

An API tester (also called an API client or REST client) is a tool that allows developers and testers to send HTTP requests to web API endpoints and inspect the responses. It is essential for API development, debugging, integration testing, and documentation verification. Unlike full-featured desktop applications like Postman or Insomnia, this online API tester requires zero installation — just open the page and start testing.

Supported HTTP Methods

How to Use This Tool

1. Enter the API URL: Type or paste the full API endpoint URL into the URL field (e.g., https://jsonplaceholder.typicode.com/posts/1).
2. Select HTTP method: Choose GET, POST, PUT, PATCH, or DELETE from the dropdown based on what operation you want to perform.
3. Add headers and body: Optionally add request headers (like Authorization or Content-Type) in the Headers tab, and a request body in the Body tab for POST/PUT/PATCH requests.
4. Send the request: Click the Send button (or press Enter) to execute the request. The tool will display the response with status code, timing, headers, and formatted body.
5. Analyze the response: Review the response status code (color-coded), response time, size, headers, and body. JSON responses are automatically formatted and syntax-highlighted.

Common Use Cases

API Development and Debugging

Test your API endpoints during development to verify they return the correct response codes, headers, and data. Quickly iterate on your API design by testing different request configurations.

Integration Testing

Verify that third-party APIs you integrate with are responding correctly. Test authentication flows, check response formats, and validate error handling before writing integration code.

API Documentation Verification

Confirm that API documentation examples actually work as described. Import cURL commands from documentation and verify the responses match what is documented.

Webhook Testing

Send POST requests with specific payloads to test webhook endpoints. Verify that your webhook handler processes different payload formats correctly.

Understanding HTTP Status Codes

• 2xx (Success): The request was successful. 200 OK means the request succeeded, 201 Created means a new resource was created, 204 No Content means success with no response body.
• 3xx (Redirection): The request was redirected. 301 Moved Permanently and 302 Found indicate the resource has moved to a different URL.
• 4xx (Client Error): There was an error with the request. 400 Bad Request means invalid data, 401 Unauthorized means missing authentication, 403 Forbidden means insufficient permissions, 404 Not Found means the resource does not exist.
• 5xx (Server Error): The server encountered an error. 500 Internal Server Error means a generic server failure, 503 Service Unavailable means the server is temporarily unavailable.

CORS and Browser-Based API Testing

Since this tool runs in your browser, API requests are subject to CORS (Cross-Origin Resource Sharing) policies. If the target API does not include Access-Control-Allow-Origin headers, the browser will block the response. Most public APIs support CORS, but internal or private APIs may not. In that case, consider testing from a backend environment or configuring the API server to allow CORS.

Frequently Asked Questions

What is an API tester?

An API tester is a tool that lets you send HTTP requests to REST API endpoints and inspect the responses. It helps developers debug, test, and verify API behavior by showing response status codes, headers, response time, and the response body in a formatted view.

Is this API tester free to use?

Yes. You get 3 free requests a day with no sign-up; Pro raises that to 60. All requests are sent directly from your browser, so your data stays private and is never stored on our servers.

Can I test APIs that require authentication?

Yes. You can add Authorization headers with Bearer tokens, API keys, or Basic authentication credentials. Simply add a header with the key "Authorization" and your token value in the headers section, or use the built-in Auth tab for convenience.

Why does my API request fail with a CORS error?

CORS (Cross-Origin Resource Sharing) errors occur when the target API server does not allow requests from web browsers on different domains. This is a server-side security policy. You can ask the API provider to add CORS headers, or use the API from a backend server instead.

What HTTP methods are supported?

This tool supports the five most common HTTP methods: GET for retrieving data, POST for creating resources, PUT for replacing resources, PATCH for partial updates, and DELETE for removing resources.

Additional Resources

• HTTP Request Methods - MDN Web Docs
• HTTP Response Status Codes - MDN Web Docs
• Cross-Origin Resource Sharing (CORS) - MDN Web Docs