REST API Tester Online
Send GET, POST, PUT, PATCH, and DELETE requests directly from your browser. Inspect status codes, latency, headers, and formatted JSON responses.
// Click "Send Request" to test an endpoint
About REST API Tester Online
The REST API Tester Online is an in-browser HTTP client engineered for testing RESTful endpoints, validating webhook routes, and inspecting JSON payloads directly from your browser. Developed as a lightweight alternative to desktop API clients, it provides an immediate environment for frontend and backend engineers to execute requests, inspect response status codes, and verify request/response lifecycles without requiring local software installations or account signups.
In modern web architectures, testing API endpoints during development is critical for verifying HTTP status responses, evaluating network latency, and validating data contracts between client applications and server interfaces. This tool executes requests using the standard browser fetch() API, giving you realistic insights into how your endpoints respond to web clients.
How to Test an API in 4 Steps
Send requests and inspect real-time responses in seconds:
- 1 Choose HTTP Method: Select your target method (GET, POST, PUT, PATCH, or DELETE) from the dropdown selector.
-
2
Input Endpoint URL: Enter the target REST API URL (e.g.
https://api.example.com/v1/users) including any necessary query parameters. -
3
Configure Headers & Body: Specify required HTTP headers (such as
Content-TypeorAuthorization) and provide JSON payloads for write requests. - 4 Execute & Inspect: Click "Send Request" to analyze HTTP response status, elapsed network time, payload byte size, and formatted JSON output.
Supported HTTP Methods & Status Code Reference
Standards-compliant REST method characteristics and common HTTP response codes:
| Method / Status | RFC Classification | Idempotency | Typical Development Use Case |
|---|---|---|---|
| GET | RFC 9110 Safe Method | Yes | Querying or retrieving resources without modifying server-side database state. |
| POST | RFC 9110 Mutation | No | Creating new database entries, submitting form data, or triggering transactional actions. |
| PUT | RFC 9110 Full Replacement | Yes | Completely replacing a target resource with the uploaded representation. |
| PATCH | RFC 5789 Partial Update | No | Applying incremental changes or updating specific fields of an existing entity. |
| DELETE | RFC 9110 Removal | Yes | Instructing the origin server to permanently remove the target resource. |
| 200 OK / 201 Created | Successful Response | N/A | Request processed successfully; 201 confirms resource creation with URI location. |
| 400 / 401 / 403 / 404 | Client Error Range | N/A | Syntax errors, invalid JSON payloads, missing API keys, or non-existent routes. |
| 500 / 502 / 503 | Server Error Range | N/A | Unhandled backend exceptions, proxy gateway failures, or temporary server overload. |
Browser CORS Realities & Proxy Architecture
Because this tester runs directly inside your web browser, all network operations are governed by the browser's Same-Origin Policy (SOP) and Cross-Origin Resource Sharing (CORS) specifications. When your browser issues an asynchronous fetch() request to a different domain, protocol, or port, the remote server must return an explicit Access-Control-Allow-Origin header.
If the remote endpoint does not permit cross-origin requests from browser origins, the browser's security sandbox intercepts and halts the response before JavaScript can inspect it. This is standard browser security behavior—not an error within this tool.
If an API endpoint rejects browser origins, toggling the CORS Proxy routes the request through a public gateway that appends compliant CORS response headers. Important Security Note: Only use public CORS proxies for public, test, or mock endpoints. Never transmit production secrets, private access tokens, or sensitive user records through public proxy relays.
Technical Specifications & Runtime Constraints
Accurate technical characteristics of this browser-based HTTP client:
| Architecture Component | Technical Implementation | Operational Characteristics |
|---|---|---|
| Networking Engine | Standard W3C Fetch API | Dispatches asynchronous HTTP/1.1 and HTTP/2 network frames via the client browser. |
| Payload Serialization | ECMA-404 / RFC 8259 JSON Standard | Supports nested JSON objects, arrays, numerical values, booleans, and null primitives. |
| Latency Measurement | High-Resolution Timer API | Network duration recorded accurately via performance.now(). |
| Data Flow & Privacy | Client Sandbox & Direct Network Transport | Requests route directly from your device to the target API host. No intermediate database logging. |
| Functional Limitations | Browser Sandbox Boundaries | Cannot establish raw TCP/UDP sockets, cannot bypass CORS without proxy, and cannot read forbidden HTTP headers (e.g. Set-Cookie). |
Frequently Asked Questions
Can I test localhost APIs with this tool?
Yes, provided your local development server (e.g. Express, Django, FastAPI, Spring Boot) enables CORS headers such as Access-Control-Allow-Origin: *. Because your browser runs on the same physical machine as your local server, requests to http://localhost:3000 or http://127.0.0.1:8000 can execute directly.
How do I pass Bearer authentication tokens or custom headers?
Enter standard JSON key-value pairs into the Headers (JSON) editor, or switch to the Bearer Auth Token tab to paste your token directly. For instance, to pass a Bearer token, add {"Authorization": "Bearer your_token_here", "Content-Type": "application/json"}.
Why does my request fail with "Failed to fetch" or a CORS error?
Modern browsers enforce cross-origin security. If the destination server does not explicitly return the Access-Control-Allow-Origin header allowing browser requests, the browser blocks the response. Enabling the CORS Proxy toggle routes the request through a public proxy to bypass this restriction for test endpoints.
Does this tool send request data to your servers?
No. In standard mode (CORS Proxy OFF), HTTP requests are dispatched directly from your browser to the destination API endpoint. We operate no intermediate telemetry or logging servers. If you enable the CORS Proxy, requests pass through a third-party public proxy service strictly to append CORS headers.
What request body formats are supported?
The Request Body panel parses and transmits valid JSON payloads. When you configure a POST, PUT, or PATCH method, the JSON body is serialized and sent with the corresponding Content-Type: application/json header.
Can I copy the API response formatted as pretty-printed JSON?
Yes. When a response contains valid JSON, the inspector automatically formats it with 2-space indentation. Clicking the "Copy Response" button instantly writes the complete formatted payload to your system clipboard.