CORS Error Diagnostic
Paste a CORS console error and get the likely cause and the server-side fix.
Paste an error and diagnose to see the likely cause and server-side fix.
Frequently Asked Questions
What does a CORS error actually mean?
The browser blocked a cross-origin request because the response lacked the right Access-Control-Allow-Origin header. It is a browser-side security enforcement, not a network failure — the server may have answered fine.
Why does it work in Postman but fail in the browser?
Postman and curl do not enforce the same-origin policy; browsers do. The missing CORS header only matters to the browser, which is why server-side calls succeed but client-side fetch fails.
What is the fastest fix?
Have the API respond with Access-Control-Allow-Origin for your origin (or *) plus any required methods/headers. Use the CORS Header Generator on this site to produce the exact Nginx or Apache config.