Test API Online — Free, No Install | Send Web Request
Test any API in your browser—no signup or install. Just send.
Testing APIs doesn't have to mean installing Postman or wrestling with curl. You can test any REST or SOAP API directly in your browser with Send Web Request. No signup, no installation, no account required. This guide walks you through what API testing is, how to test APIs online step by step, and how to fix common issues like CORS and 401 errors.
What is API testing?
API testing means sending HTTP requests to an API and checking the responses. You verify that the endpoint returns the right status code, headers, and body. When you're building or integrating with an API, you need to test that it works: maybe you're debugging a webhook, checking a new endpoint, or teaching someone how HTTP works. You send a request (e.g. GET or POST), inspect the response, and fix any issues. That's API testing.
Ways to test APIs: curl, Postman, and browser tools
You can test APIs in several ways. curl is the command-line standard: you type a curl command with URL, method, and headers. It's powerful but requires learning the syntax and using a terminal. Postman and similar desktop clients offer a GUI: you fill in method, URL, headers, and body and click Send. They often require installation and sometimes an account. Browser-based API testers run entirely in a tab: no install, no signup. You open a webpage, enter your request, and send. Tools like Send Web Request give you the same core capability—send a request, see the response—from any device with a browser.
Why test APIs online in your browser?
A browser-based tester works everywhere: your work laptop, a shared computer, a tablet, or a machine where you can't install software. There's nothing to update or configure. You can start testing in seconds. For quick checks, demos, or learning HTTP, an online API tester is often faster than opening Postman or writing a curl command. Your data can stay in your browser too—many tools, including Send Web Request, don't log your URLs or request bodies.
Step-by-step: how to test an API online
Open Send Web Request (or any browser-based API tester). Choose the HTTP method: GET for reading data, POST for creating or submitting, PUT or PATCH for updating, DELETE for removing. Enter the API URL in the address field. Add any query parameters in the URL or in a dedicated params editor. Add headers if needed: Content-Type for the body format, Authorization for auth tokens. For POST, PUT, or PATCH, enter the request body (e.g. JSON or XML). Click Send. The tool shows the response status code, response headers, and body. Use that to verify the API behaves as expected.
Example: Testing a GET endpoint
To test a simple GET request, enter the URL and click Send. GET requests don't have a body; parameters go in the URL. For example, to fetch a list of users from a public API:
GET https://jsonplaceholder.typicode.com/usersExample: Testing a POST with JSON
Many APIs expect JSON in the body. Set the method to POST, add the header Content-Type: application/json, and put your JSON in the body. Example:
POST https://jsonplaceholder.typicode.com/posts
Content-Type: application/json
{
"title": "Test Post",
"body": "This is a test",
"userId": 1
}Troubleshooting: CORS errors
If you see a CORS error in the browser console, the API is blocking requests from your origin. The server must send headers like Access-Control-Allow-Origin to allow your domain. When testing from a browser tool, you're sending the request from the tool's origin, so some APIs will block it. Two options: (1) Use proxy mode in Send Web Request—the request goes through our server so the API sees a different origin and CORS may no longer block you. (2) Test CORS behavior: send the request and inspect the response headers to see what the server allows. Use our CORS test page to send cross-origin requests and view the CORS headers.
Troubleshooting: 401 Unauthorized
A 401 response means the server requires authentication. You need to send credentials, usually in an Authorization header. For Bearer tokens: add the header Authorization: Bearer YOUR_TOKEN. For Basic auth: use Authorization: Basic base64(username:password). Check the API docs for the exact format. In Send Web Request, add the header in the headers section and send again. If you still get 401, the token may be expired or the header name may differ (e.g. X-API-Key). See our Authorization header guide for details.
Troubleshooting: Wrong Content-Type or 415
If the API returns 415 Unsupported Media Type or rejects your body, the server didn't accept the format you sent. Set the Content-Type header to match what the API expects: application/json for JSON, application/xml or text/xml for XML, application/x-www-form-urlencoded for form data. The body must match: valid JSON for application/json, key=value for form-encoded. Fix the header and body, then send again.
Comparing curl and a browser API tester
The same request can be sent with curl or with a browser tool. For example, a GET with a Bearer token in curl:
curl -X GET "https://api.example.com/users" \
-H "Authorization: Bearer YOUR_TOKEN"
Same request in Send Web Request
In the tool: set method to GET, URL to https://api.example.com/users, and add a header Authorization with value Bearer YOUR_TOKEN. Click Send. You get the same response. The browser tool is easier for one-off tests and for people who prefer a form over the command line; curl is better for scripts and automation. Both are valid ways to test an API online.
Try it now
Open Send Web Request and test your API. When you use the tool without an account, your request data stays in your browser—we don't store it. The core tool is free and works with any REST or SOAP API. Optional Cloud Sync (save requests to the cloud) requires an account and subscription. Use the API testing tool for a product overview, or stay here for more guides and examples.