API Tester - Test & Debug REST APIs Online Free

A full-featured browser-based HTTP client — like Postman, without the install. Send requests, inspect responses, manage collections, use environment variables, and generate code snippets.

ENV

Request

KeyValue

Auth type

Type

KeyValue

Assertions run automatically after each request. Pass/fail shown below the response.

Collections

History

Response

Enter a URL and click Send to see the response here.

Tip: Use in your URL and set it in Environment Variables.

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About the API Tester

The ToolBrainy API Tester is a free, browser-based HTTP client for developers and QA engineers. Test REST and JSON APIs instantly — no sign-up, no installation, no server. Supports all major HTTP methods, query parameters, custom headers, five authentication types (Bearer Token, Basic Auth, API Key, OAuth 2.0), and six body formats. Environment variables let you switch between development, staging, and production endpoints with one click. The built-in code generator exports your request as cURL, JavaScript Fetch, Axios, Python Requests, PHP cURL, or Node.js. All data stays in your browser — nothing is sent to ToolBrainy servers.

How to Use the API Tester

1

Set up environments — click Manage Variables to define , , or any key. Switch between Development, Staging, and Production instantly.

2

Build your request — select an HTTP method, enter the URL, then configure query params, headers, authentication, and request body in the matching tabs.

3

Click Send — the response appears on the right with syntax highlighting, status code, response time, and size. Switch between Pretty, Raw, Headers, and Cookies views.

4

Generate code — open the Code tab to copy a ready-to-run snippet in cURL, Fetch, Axios, Python, PHP, or Node.js. Save frequent requests to Collections.

Why Use This API Tester

All HTTP methods — GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS in one place.

Environment variables — switch base URLs, tokens, and API keys between environments without editing every request.

5 auth types — Bearer Token, Basic Auth, API Key, OAuth 2.0 client credentials, or no auth.

Code generation — export as cURL, Fetch, Axios, Python, PHP, or Node.js with one click.

Collections and history — save requests, import/export Postman collections, replay from history.

Automated tests — add assertions (status code, body content, headers) that run after every request.

Use Cases

✓

API development and debugging — test new endpoints as you build, without leaving the browser.

✓

QA and integration testing — verify third-party APIs, add assertions, and catch regressions fast.

✓

Learning REST APIs — an ideal sandbox for students and beginners exploring how APIs work.

✓

Code snippet generation — generate language-specific client code from any tested request.

Frequently Asked Questions

Is this API tester free?

Yes, completely free with no sign-up or installation required. All requests are sent directly from your browser using the Fetch API.

Are my requests stored on a server?

No. All request data, collections, history, and environment variables are stored locally in your browser's localStorage. Nothing is sent to ToolBrainy's servers.

How do environment variables work?

Click "Manage Variables" to define key-value pairs like base_url = https://api.example.com. Then use in your URL, headers, or body. Switch environments (Development, Staging, Production) in the top bar.

Why do some requests fail with a CORS error?

Browser-based HTTP clients are subject to CORS restrictions enforced by the target server. If the server doesn't include the required CORS headers, the browser blocks the response. This is a server-side limitation, not a bug in the tool.

Can I import a Postman collection?

Yes. Click "Import" in the Collections section and paste your exported Postman Collection JSON (v2.0/v2.1). Requests will appear in the Collections list.