What is a CORS preflight request?
Non-simple requests trigger an OPTIONS preflight first. The server must return correct CORS headers for both OPTIONS and the actual request.
CORS Checker
DevTools CORS Checker inspects Access-Control-Allow-Origin and related response headers for a URL via server proxy—to diagnose browser cross-origin blocks.
CORS Checker
Check whether a URL returns correct CORS response headers and diagnose cross-origin access issues.
About this tool
Frontend calls to third-party APIs often fail when CORS headers are missing. Enter an API URL to see relevant headers and guidance.
How to use
- Enter the URL to check.
- Click Check CORS.
- Adjust server headers based on the results.
FAQ
Is Allow-Origin: * safe?
Fine for public read-only APIs. With cookies or sensitive data, specify exact origins—Allow-Credentials cannot be used with *.
Is the checked URL stored?
The check uses a server route for the request; URLs are not kept as persistent history.
Is this tool free?
Yes. No registration required.
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