Why not just read headers from the browser?

The browser hides outgoing request headers from JavaScript for security. The only way to see the full set is to ask a server what it actually received.

What is X-Forwarded-For?

It is a header added by proxies and CDNs listing the chain of client IPs. If you see one, your request passed through at least one reverse proxy.

Does this include cookies?

Cookies are a header (Cookie:) but this tool intentionally does not display cookie values. It shows that the header was sent and its byte length only.

HTTP Headers Viewer

API

Fetching your HTTP headers…

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The HTTP request headers your browser sends, as seen by the server. Grouped by category with explanations.