Here's one of the first extensions to use the new webRequest API in Chrome 17. It watches as the browser downloads a webpage, picks out various bits of protocol-related information, and squishes it down into a convenient table. Everything's captured and displayed privately, without creating any additional network traffic. The first thing you'll see is an icon in the location bar. A large 4 or 6 shows whether the outer page was fetched using IPv4 or IPv6. If the page contains elements from other domains, then smaller numbers will appear alongside for those. When you click the icon, a table pops up, containing a row of information for each domain: - A padlock icon, for HTTP, HTTPS, or a mix of both. This is helpful for tracking down mixed content warnings, but you shouldn't treat it as absolute security advice. - The IPv4 or IPv6 address. If connections span more than one IP, then the most recent one wins. When the connection is still open, the address is highlighted in yellow. - A "cached" symbol. This mainly exists to warn you that no actual connections took place, so the IP address might be stale. - An "S" for WebSocket handshakes in Chrome 58+. For convenient copying, clicking on a hostname or address will select it. There's also a right-click option to look up IP addresses with bgp.he.net. I'm not affiliated with that service, but it's my personal favorite. IPvFoo is Free Software (Apache 2.0 license).