Learn CORS

Follow these guides in order, then use the tester and quiz to check what you learned. Examples use fictional origins; adapt them to a frontend and API you control.

1. What CORS grants: response access
2. Origins: scheme, host, port and site
3. The same-origin policy: reads and writes
4. Simple requests and preflight triggers
5. Follow OPTIONS and the actual response
6. CORS headers and response exposure
7. Credentials, cookies and Authorization
8. Debug a real request in DevTools

Browse all concepts · Configure a framework · Check response headers · Take the quiz