API Tester – Test REST API Endpoints Online Free
Send GET, POST, PUT, DELETE, and PATCH HTTP requests directly from your browser. Inspect status codes, response headers, JSON payloads, and execution metrics in real-time.
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Comprehensive Guide to Testing REST APIs Online
Representational State Transfer (REST) APIs are the fundamental building blocks of modern web and mobile applications. Whether microservices communicate across distributed cloud networks, single-page applications (SPAs) fetch backend resources, or third-party webhooks receive payment event notifications, API reliability and contract precision are paramount.
Our Client-Side Online API Tester provides developers, QA engineers, and system architects with a lightweight, browser-based alternative to heavy desktop applications like Postman or Insomnia. You can execute HTTP requests, inspect JSON response structures, evaluate response latency, and test authentication headers in real-time with zero software installation.
Key HTTP Request Methods Explained
Understanding HTTP verbs is fundamental to designing and debugging RESTful interfaces:
- GET: Requests data from a specified resource without altering server state. Essential for fetching user profiles, catalog lists, and resource details.
- POST: Submits data to the server to create a new resource entity (e.g., submitting a contact form, registering an account, or placing an order).
- PUT: Overwrites and replaces an existing target resource completely with the submitted request payload.
- PATCH: Applies partial modifications to a resource, updating only the specific fields supplied in the request body.
- DELETE: Removes the designated resource from the database or storage layer.
HTTP Response Status Codes Quick Reference
| Status Range | Category | Common Examples |
|---|---|---|
2xx |
Success | 200 OK, 201 Created, 204 No Content |
3xx |
Redirection | 301 Moved Permanently, 302 Found, 304 Not Modified |
4xx |
Client Errors | 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found |
5xx |
Server Errors | 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable |
Understanding Browser CORS Constraints
When issuing API calls directly inside a web browser using JavaScript's fetch() API, you may occasionally encounter cross-origin errors (e.g., Failed to fetch or CORS policy block). This occurs when the destination API server lacks standard Cross-Origin Resource Sharing headers such as Access-Control-Allow-Origin: *. For public endpoints or servers configured with CORS headers enabled, requests execute seamlessly.
Frequently Asked Questions (FAQs)
Q: Are my API tokens or request bodies stored on your server?
A: Absolutely not. Our API Tester is built 100% client-side. Requests are initiated directly from your web browser to the endpoint URL. No API keys, credentials, or payloads touch our web servers.
Q: Why did my request fail with a CORS error?
A: Web browsers enforce Cross-Origin Resource Sharing (CORS) security policies. If the API endpoint you are testing does not permit cross-origin requests from web clients, the browser blocks the response. Ensure your API server sends appropriate Access-Control-Allow-Origin response headers.
Q: How can I pass Authorization tokens?
A: Simply switch to the Headers tab, click "+ Add Header", enter Authorization as the Header Key, and provide your token (e.g., Bearer eyJhbGci...) as the Header Value.