~/tools / 12 / cors-preflight-options
CORS Headers Inspector
CORS failures are diagnosed by reading headers, so learn the three shapes by heart: the permissive wildcard 204 that unblocks everything, the credentialed setup where Allow-Origin must name one exact origin (wildcards break withCredentials), and the misconfigured response missing Access-Control-Allow-Origin — the one producing that red console error you were just googling.
— validating —
$ man cors-preflight
Everything above is encoded into the #data= fragment of the exported URL — deflated and base64url-packed by your browser. Fragments are never sent to any server, so this mock is shareable and private. Paste the URL anywhere: a teammate's browser decodes it identically.
grep -i related-searches
- cors preflight response example
- access-control-allow-origin test
- simulate cors error
- options request headers mock
- cors allow credentials example