Free CORS debugger. Test CORS headers, fix Access-Control-Allow-Origin errors, and debug preflight requests. See how servers respond to Origin headers instantly.
The CORS Debugger on httpstatus.com simulates preflight and simple cross-origin requests against any endpoint, revealing exactly which Access-Control headers are present, missing, or misconfigured. It tests combinations of origins, methods, and custom headers, then reports whether the browser would allow or block each scenario. The tool highlights common pitfalls like wildcard origins combined with credentials, missing Access-Control-Max-Age that trigger repeated preflights, and overly restrictive allowed-method lists.
Frontend developers integrating third-party APIs from single-page applications, backend engineers configuring gateway CORS policies, and QA testers verifying cross-domain functionality across staging environments all benefit from deterministic CORS simulation. Results include a corrected header configuration you can copy directly into your server config. Everything runs client-side on httpstatus.com, so your origin and credential details remain private throughout the debugging session.