Free tools
CORS Header Checker
CORS header checker. Evaluate Access-Control-Allow-Origin/Methods/Headers/Credentials and estimate whether a request (incl. preflight) is allowed.
Request
Used for preflight checks. Include header names only (not values). Leave blank if you don’t send custom headers.
Response headers
Result
CORS header checker
Paste the relevant Access-Control-* response headers and this tool estimates whether a browser would allow the cross-origin request. It also highlights common pitfalls like credentialed requests with Access-Control-Allow-Origin: *.
When this helps
- Debug “CORS blocked” errors from the browser console
- Validate preflight requirements (methods + headers)
- Check whether cookies/credentials are allowed
How to use
- Enter the browser Origin and intended request method/headers.
- Paste the server’s CORS response headers (or expected values).
- Click Check CORS and review errors/warnings.
Note
This is a deterministic checker, not a network test. Real behavior can differ based on exact requests, redirects, and server behavior.