Fiddler on the Roof

If you haven’t already heard of this tool, called Fiddler, you should try it. http://www.fiddler2.com/fiddler2/

Fiddler attaches itself to any WinInet application (IE and other MS products) and all other networking applications can be configured to use it as a proxy.

It records every networking operation and actually allows breaking on operations and changing the packet contents (or HTTP contents) on outgoing and incoming transactions. You can analyze the packet contents using several filters and tools.

But what I love the most about it is that it’s totally programmable, and scriptable. You can use JScript.Net to play with the headers content
(I’ve been playing with it over the last couple of days, using a script to add a FollowTX header to HTTP transactions going out of Firefox) or write .Net plugins.

Not only is it absolutely free, but it is recommended by Microsoft for web developers, to test load and security of web applications.

Enjoy