Fiddler PowerToy – Powerful HTTP Debugging in IE

Internet Explorer Developer Center: Fiddler PowerToy – Part 1: HTTP Debugging
Have you ever found yourself wondering how Microsoft Internet Explorer interacts with your Web application? Have you encountered a strange performance bottleneck that you can’t track down? Are you curious about which cookies are being sent, or what downloaded content is marked as cacheable?

Microsoft Fiddler can help you answer these questions, and many more. Fiddler is an HTTP debugging proxy that logs all HTTP traffic between your computer and the Internet. Fiddler enables you to inspect all HTTP traffic, set breakpoints, and “fiddle” with incoming or outgoing data. Fiddler is much simpler to use than NetMon or other network debuggers because it exposes only HTTP traffic and does so in a user-friendly format.

Fiddler includes a simple but powerful Microsoft JScript .NET event-based scripting subsystem flexible enough to support a broad array of HTTP debugging tasks. Written in C# on the Microsoft .NET Framework, Fiddler is available as an unsupported PowerToy for Internet Explorer.

Does a lot of the things that the developer extenisons to Firefox do, but as a system proxy. You can even set Firefox to proxy thru it to get the same info. It is interesting to see the way sites can react to the different browsers. Download Fiddler here.