I was having a problem understanding the actual content of HTTP requests I was sending from my Xcelsius model and what I was getting back. The gods of development must have been watching over me because just as I thought, "There must be a really good monitoring proxy for this kind of stuff," my friend Rumico, who runs the excellent Everything Xcelsius Web site, posted an article on the LinkedIn Xcelsius Gurus group about a tool called .

Fiddler, written by Eric Lawrence (a Microsoft employee though this is not a Microsoft product), is described as "a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and 'fiddle' with incoming or outgoing data."

Fiddler, which is for Windows only, can be used with any application that supports proxying and, best of all, it's free.

Installation is simple and Internet Explorer gets a Fiddler option in the tools menu while Firefox gets a Fiddler menu embedded in its status bar.

The left panel of the Fiddler interface lists all the captured transactions that have been routed (these can also be saved and reloaded) and clicking on a single transaction in the list displays a detailed analysis on the user interface's right panel.