CORS Checker

What is CORS?

CORS (Cross-Origin Resource Sharing) is a security mechanism that allows web pages to make requests to a different domain than the one serving the web page. Browsers enforce the same-origin policy by default, which prevents JavaScript from making requests to different origins. CORS headers tell the browser which origins are allowed to access resources.

Our free CORS Checker helps you verify CORS configuration for any URL. While browser restrictions limit full header inspection, our tool attempts to determine if CORS is enabled and provides guidance on checking CORS headers using browser developer tools.

Why Check CORS?

Checking CORS is important for:

• Verifying API accessibility from web applications
• Debugging cross-origin request issues
• Ensuring proper CORS header configuration
• Testing API endpoints for frontend integration
• Security analysis and configuration review

CORS Headers

• Access-Control-Allow-Origin: Specifies allowed origins (* or specific domain)
• Access-Control-Allow-Methods: Allowed HTTP methods (GET, POST, etc.)
• Access-Control-Allow-Headers: Allowed request headers
• Access-Control-Allow-Credentials: Whether credentials can be included
• Access-Control-Max-Age: How long preflight results can be cached

Common CORS Issues

• No CORS Headers: Server doesn't send CORS headers
• Wrong Origin: Access-Control-Allow-Origin doesn't match request origin
• Missing Methods: Required HTTP methods not allowed
• Credentials Issue: Credentials not allowed when needed

Best Practices

• Use Specific Origins: Avoid using * for Access-Control-Allow-Origin
• Allow Only Needed Methods: Restrict allowed HTTP methods
• Handle Preflight: Properly handle OPTIONS preflight requests
• Test Thoroughly: Test CORS from different origins
• Use Browser Dev Tools: Inspect CORS headers in Network tab

FAQs

What is a preflight request?

A preflight request is an OPTIONS request sent by the browser before the actual request to check if CORS is allowed.

How do I enable CORS on my server?

Configure your server to send Access-Control-Allow-Origin and related headers. The exact method depends on your server framework.

Can I use * for Access-Control-Allow-Origin?

Using * allows all origins but doesn't work with credentials. Use specific origins for better security.

Why do I get CORS errors?

CORS errors occur when the server doesn't send proper CORS headers or the origin isn't allowed.

How do I check CORS headers?

Open browser developer tools, go to Network tab, make a request, and check the Response Headers for Access-Control-* headers.