Freeware Descriptions:
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.
Here is complete features (taken from authors site):
Fiddler is freeware and can debug traffic from virtually any application, including Internet Explorer, Mozilla Firefox, Opera, and thousands more. Fiddler 2 has replaced Fiddler 1.x. Fiddler 2 supports debugging HTTPS traffic, a richer extensibility model, and can by installed side-by-side with Fiddler 1.x if desired.
Requires Microsoft .NET Framework 2.0.

File Size / OS:
- 505 KB / Windows 9x - ME - 2000 - NT - XP - 2003 - Vista
Download Microsoft Fiddler 2.2.2.0: