HTTP headers / request header
X-Forwarded-For
X-Forwarded-For: 203.0.113.7, 70.41.3.18
What it does
The de-facto chain of client IPs appended by each proxy hop. The leftmost entry claims to be the original client.
The gotcha
Trivially spoofable by the client — only trust the entries YOUR proxies appended, or use the standardized Forwarded header.
Debugging headers on a phone
The fastest way to see what X-Forwarded-For is actually doing is to send the request and read both sides raw — ReqPad shows auto-generated and custom headers for every request, on all six protocols, with history. Related references: status codes · Authorization · Accept · Accept-Encoding · Accept-Language · If-None-Match · If-Match
Inspect X-Forwarded-For on a live request.
Build the request, send it, read raw headers and timing — from your iPhone. Free to start.