API Response Tester

What is an Online API Tester?

An online API tester is a browser-based tool for sending HTTP requests — GET, POST, PUT, PATCH, DELETE — to any REST endpoint and inspecting the response. It functions like a lightweight Postman alternative, letting you test APIs without installing any software or configuring a local environment.

How to Use the API Tester

1. Select an HTTP method (GET, POST, PUT, PATCH, or DELETE) from the dropdown.
2. Enter the full API endpoint URL in the URL field.
3. Add or modify request headers — for example, set Authorization: Bearer <token> for protected endpoints.
4. For POST, PUT, or PATCH requests, enter a JSON request body in the body field; click Format JSON to pretty-print it.
5. Click Send to execute the request.
6. Inspect the response — view the status code, response time in milliseconds, and the full JSON body.

Common Use Cases

• Quickly verifying that a public REST API is up and returning expected data.
• Debugging authentication issues by testing different Authorization header values.
• Prototyping API integrations before writing application code.
• Checking CORS behaviour from the browser during front-end development.
• Demonstrating API endpoints to stakeholders without sharing Postman collections.
• Testing webhook endpoints by simulating POST payloads from a third-party service.

Why Use an Online REST API Tester?

Desktop tools like Postman and Insomnia are powerful but heavyweight — they require installation, sign-in, and sync setup before you send your first request. An online API tester removes all that friction. Open the page, type a URL, and hit Send within seconds. It is ideal for quick spot-checks, sharing reproducible test cases via a URL, or working from a machine where you cannot install software. Response times are measured in the browser using the Performance API, giving you accurate latency data for the network hop from your machine to the server.

Frequently Asked Questions

Can I test APIs that require authentication?

Yes. Add an Authorization header with your Bearer token, API key, or Basic auth credentials in the Headers section. The tool passes all custom headers directly with the request, so any authentication scheme that works via HTTP headers is supported.

Why does my API request fail with a CORS error?

CORS errors occur when the target server does not include the appropriate Access-Control-Allow-Origin header in its response. This is a server-side restriction and cannot be bypassed by the client. For APIs that block browser-origin requests, you'll need to proxy the request through a server-side environment or use a CORS proxy service.

Is the request body sent for GET requests?

The body field only appears for POST, PUT, and PATCH requests, as these are the standard methods that carry a request body. GET and DELETE requests are sent without a body, which matches the HTTP specification and how most servers expect these methods to behave.

Related Tools

Explore more free developer tools: JSON Formatter — validate and pretty-print the JSON responses you receive. JWT Decoder — decode and inspect JWT tokens used in API authentication. URL Encoder — encode query parameters before adding them to your API requests.