Yes, Fiddler is wonderful
For some reason this week literally 5 people emailed me to tell me how great Fiddler is and that they wonder why it's not on the Ultimate Tool List. Well, to be clear, both Fiddler and Eric Lawrence are the bomb. Fidder is basically an "HTTP Debugger" (implemented as a local proxy) has a nice eventing system to support scripting. Why haven't I used it? I just haven't really needed it. Nearly all my debugging of HTTP/ASP.NET has been done happily with the simple elegance of ieHttpHeaders with the occasional use of TamperIE. Certainly my tools are simple while Fiddler is very rich in functionality so it's not really fair to compare them. I see from the Fiddler page that you can really mess with HTTP Headers and what-not with Fiddler. That said, I'm going to download the new release from last week and give it some mindshare as this tool has definitely struck a chord with many folks.