Web

CORS Header Debugger

Paste request/response headers and diagnose CORS mismatches.

Free online cors header debugger — runs entirely in your browser. Nothing is sent to our servers.

Paste preflight / response headers to explain common CORS failures.

Request headers

Response headers

Diagnosis

[ok] No CORS mismatches detected from pasted headers

About this tool

Use this free browser-based cors header debugger when you need a quick web utility without installing software. Processing stays on your device for privacy. Related searches: cors, origin, headers, preflight, access-control.