CORS Tester – Test Cross-Origin Resource Sharing Free Online
Test CORS headers for any URL. Check if a server allows cross-origin requests and inspect Access-Control headers. Free CORS checker.
What is CORS Tester?
CORS (Cross-Origin Resource Sharing) is a browser security mechanism that controls how web pages can request resources from a different domain. When a browser makes a cross-origin request, the server must include the correct Access-Control headers for the request to succeed. Our CORS Tester checks whether a URL has proper CORS headers configured, helping developers debug cross-origin issues.
How to Use CORS Tester
- 1Enter the URL you want to test for CORS support.
- 2Enter the origin domain that will make the request (e.g., https://yourdomain.com).
- 3Click Test CORS to send a preflight request.
- 4Review the Access-Control headers returned by the server.
- 5Check whether CORS is properly configured for your use case.
Key Features
- ✓CORS preflight request simulation
- ✓Access-Control header inspection
- ✓Origin-specific CORS testing
- ✓Detailed header breakdown
- ✓Instant results
Benefits
- →Debug CORS errors in API integrations
- →Verify API servers have correct CORS configuration
- →Understand which origins are allowed by a server
- →Save development time diagnosing cross-origin issues
Why Use Irreva for CORS Tester?
Frequently Asked Questions
What is CORS?
CORS (Cross-Origin Resource Sharing) is a browser security mechanism that restricts how JavaScript code in one origin (domain) can make requests to a different origin. For example, code running on app.example.com cannot fetch data from api.other.com unless the API explicitly allows it via CORS headers.
What does 'Access-Control-Allow-Origin' mean?
This header in the server's response tells the browser which origins are allowed to read the response. A value of '*' allows any origin. A specific value like 'https://app.example.com' restricts access to that origin only.
What is a CORS preflight request?
For certain requests (non-GET/POST, or those with custom headers), the browser first sends an OPTIONS request to check whether the server allows the actual request. This is called a preflight. The server must respond with the appropriate allow headers for the actual request to proceed.
Why does my API work in Postman but not in the browser?
Postman does not enforce CORS because it is not a browser. CORS is a browser-only security policy. If your API works in Postman but fails in the browser, the server is not sending the correct CORS headers for your frontend's origin.
How do I fix a CORS error?
The fix must be on the server side. Add the appropriate Access-Control-Allow-Origin header to your API responses. If using Express.js, the 'cors' npm package handles this easily. For nginx, add the header in your server block. If you do not control the server, use a backend proxy to forward requests.
What is a CORS error?
A CORS error occurs when a browser blocks a cross-origin request because the server did not include the required Access-Control-Allow-Origin header in its response.
What is a preflight request?
A preflight request is an OPTIONS HTTP request that browsers send before certain cross-origin requests to check if the server will allow them. The server must respond with appropriate Access-Control headers.
Why does CORS only apply to browsers?
CORS is enforced by browsers to protect users from unauthorized cross-origin requests. Server-to-server requests (like from Node.js or curl) are not affected by CORS policies.
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