Proxy headers
Proxy headers such as Via and X-Forwarded-For are added by some proxies and can reveal to websites that a request did not come directly from you.
What proxy headers are
When an HTTP proxy forwards a request, it may add headers that describe what it did. The standard ones are Via, which names the proxy software and protocol version, and Forwarded, which records the original client address. Older, non-standard headers carry the same information: X-Forwarded-For with the client's IP, X-Real-IP, Client-IP, X-Proxy-ID, and Proxy-Connection. Corporate gateways, caching proxies, some mobile carriers, and poorly configured public proxies all add them.
A proxy that adds these headers while still showing its own address is called non-anonymous or transparent. One that forwards the request without them is anonymous. Neither term says anything about the quality of the IP address; they only describe the headers.
Why it matters
Any website can read these headers. If X-Forwarded-For contains your real address, the proxy has handed it over on every request, and no amount of browser tuning helps. Even a Via header without an address is a disclosure: it says a proxy is present, which prompts extra checks. Our anonymity score deducts 10 points when the request carries any of the headers listed above.
Note that reverse proxies and content delivery networks in front of a website also add X-Forwarded-For, but on the server side; we read only the headers that arrive from your side of the connection.
How to check
The HTTP headers tool shows every header your browser's request carried, exactly as our server received it, with proxy-related headers highlighted. The proxy checker combines that check with the network classification of your address. Run them with the proxy active and, for comparison, without it.
How to fix it
Switch to a proxy that does not add forwarding headers; SOCKS5 proxies never add HTTP headers because they do not look inside the HTTP stream. If you run your own proxy server, disable the Via and X-Forwarded-For options in its configuration. For VPN connections this signal does not apply, since the tunnel carries your packets unchanged and the VPN server does not rewrite HTTP.
A common misconception
The absence of proxy headers does not make an address anonymous. The address itself can still be classified as datacenter or VPN-provider space, and browser leaks can still reveal the real address. Headers are one signal out of twelve on our score page.