A new version of Fiddler came out recently. From the Fiddler home page:

Fiddler is a HTTP Debugging Proxy which logs all HTTP traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP traffic, set breakpoints, and “fiddle” with incoming or outgoing data. Fiddler includes a powerful event-based scripting subsystem, and can be extended using any .NET language.

Fiddler is freeware and can debug traffic from virtually any application, including Internet Explorer, Mozilla Firefox, Opera, and thousands more.

I use Fiddler all the time in my work. I find it invaluable for debugging AJAX requests, performance metrics, file sizes, and more. I’ve used it to see what web service calls Flash applications make. I like the fact that it works with any web browser. It also supports FiddlerScripts that allow you to impersonate user agents, simulate a dial-up connection, execute performance tests, or modify HTML as it’s downloaded.

If you need to debug HTTPS/SSL traffic, or you want to save browsing sessions as Visual Studio WebTest files, you can install Fiddler2. I wish they didn’t name Fiddler2 “fiddler 2“, because it makes it sound like it’s a new version of Fiddler 1.2, when it’s not. Fiddler2 is just a fork of Fiddler that’s been ported to .NET 2.0 & allows for debugging SSL.

Screenshot of Fiddler Chart