Inspect browser signals and fetch response headers from an HTTP or HTTPS URL. Access depends on the remote CORS policy; JavaScript cannot read every header or redirect.
Browser signals — inspect values exposed by your browser
URL inspection — fetch a URL and inspect accessible response headers
CORS diagnostics — check whether the browser can access the response
Cache and redirect headers — inspect exposed Cache-Control, Location and other headers
Browser signals visible to JavaScript
This is not the full set of HTTP request headers: some headers are not exposed to JavaScript.
Inspect response headers for a URL
Note: If the request reports "Failed to fetch" the remote site may not allow browser access through CORS. Network failures can also cause fetch errors. Only browser-accessible headers are displayed.
Learn more: MDN: Introduction to CORS
