Elite proxy (high anonymity)

To a website, a request through an elite proxy looks, by its headers, no different from a request by an ordinary visitor with the proxy's address. There is neither Via nor X-Forwarded-For.

The anonymity levels, transparent, anonymous and elite, describe only headers. They do not promise that a site will not detect a proxy in other ways.

Other signs remain: the network type by ASN, the address history, the browser fingerprint and whether the time zone matches the country.

You can check which address and country websites see through your proxy on the My IP page.

How a checker decides that a proxy is elite

A checker sends a request through the proxy to its own test server. The server compares the address of the incoming connection with the proxy address and lists all the headers that came with the request. If the connection came from the proxy address and there are no Via, X-Forwarded-For, Forwarded or similar headers, the proxy is marked elite.

Run the check from the same program and with the same settings you work with. A browser extension and a script may take different routes, and a result for one says nothing about the other.

Clean headers, but the site still sees a mismatch

The elite level covers headers only. The rest of the picture is collected by the browser itself, and it is worth checking on the My IP page in the same profile.

More on the first two signals is in the WebRTC leak and DNS leak articles. When all three points agree with the address, headers stop being the weak spot, and the network type and IP reputation come to the front.

When the header question does not arise at all

A SOCKS5 proxy passes bytes unchanged and by design does not add HTTP headers. So with port 824, or a SOCKS5 connection on a port from the 10000-20000 range, the anonymity level by headers is not an issue. For HTTP on port 823 a check over plain HTTP makes sense, and it is worth repeating after you change the program, the extension or the proxy type.