I’ve been debugging HTTP for years using trusty text-based tools like telnet and nc, but today a quasi-technical person stopped by my cube to ask for help with a caching problem and they really needed a GUI-based solution.
LiveHTTPHeaders lets you open up a separate window or tab to display HTTP headers in real time (while pages are being downloaded from various websites). It makes it pretty easy to see the various caching headers (like Cache-Control, Expires, and Pragma) and also follow trails of 302 redirects, Cookies, etc.
It also adds a cute Headers tab to the Page Info dialog box for information about the currently active page:
Absolutely brilliant. Probably something I’ll use at least once a week.