Fiddler – Web Debugging Proxy

Most people remain unaware of precisely how their web application is interacting with the web browsers that their clients have installed. If analytics are present on the site then the number of requests ending in a 404 status (File not found) may be logged but identifying precisely why the client was requesting a page in the first place may be difficult or impossible.
This is where Fiddler, a free tool, can simplify the process substantially. Fiddler is a HTTP Debugging Proxy which logs all HTTP traffic between your computer and the Internet.

It logs those requests and the responses to allow you to see what is working and what isn’t working.

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.

Fiddler is freeware and can debug traffic from virtually any application, including Internet Explorer, Mozilla Firefox, Opera, and thousands more.

Fiddler will give you a quick graph of data transferred during a session by File type.

It’s great for examining the request and response headers for cookies and Form Data.

It doesn’t do anything too exciting for images, but it does display them right within the tool so you know what image you’re dealing with.

It even lets you make custom HTTP requests right from within Fiddler. Better yet, you can use a previous request as a template and then modify it however you’d like. You can clone a prior request by dragging & dropping a session from the web session list.

You can install fiddler from http://www.fiddlertool.com/