Showing the visitor's IP

A page can show a visitor their own IP address. Two things make this work:

[% client_ip %]: a Template Toolkit variable holding the visitor's IP. It is the first hop of the X-Forwarded-For header (the real client when the site is behind a reverse proxy) if present, otherwise the direct connection address REMOTE_ADDR.
nocache: true: the IP is different for every visitor, so the page must render fresh each time. nocache: true in the front matter renders on every request and never caches, so each visitor sees their own IP (a cached page would show whoever loaded it first).

Simplest: show it directly

A whole page that renders the IP live:

---
title: Your IP
nocache: true
---

Your IP address is **[% client_ip %]**.

Keep a page cached, fetch the IP with JavaScript

To show the IP on a page you want to keep cached (fast), put the IP behind a small live endpoint and fetch it client-side. The endpoint is a nocache API page that returns JSON; the display page stays cacheable and only the IP is fetched live.

The endpoint - save as whatismyip.md (served at /whatismyip):

---
api: true
nocache: true
content_type: application/json
---
{"ip": "[% client_ip %]"}

The display page (or any theme/layout) fetches and renders it:

<p>Your IP address is <span id="your-ip">…</span>.</p>

Behind a reverse proxy

client_ip prefers X-Forwarded-For so a proxied site reports the real visitor, not the proxy. That header is only trustworthy if your edge (Apache / nginx) sets it from the real connection and strips any client-supplied copy - the same requirement as the X-Remote-* trust headers. If the site is served directly (no proxy), client_ip is the connection address and needs no configuration. The value is sanitised to IP characters before rendering, so a spoofed header cannot inject markup into the page.