Firstly, if your a Web Developer, then, like me you get extremely annoyed when having to fix JavaScript and working with slow FTP or an external client – unlike HTML and CSS, JavaScript cannot be edited on the fly, neither are there any useful tools for modifying the JavaScript ready for a page load/reload.
Similarly, sometimes you just want to make a site function a little different than it was intended, perhaps drop some useful links into a game to speed up your play – or change the style so usability is better.
This is where Fiddler comes in handy, it allows you (amongst other things) to trick any browser into thinking it is fetching a file from a website, when in fact the file could be on another website, or even on your machine!
This opens a world of possibility to Web Developers wanting to test new JavaScript but have to go through a tedious chain of management to commit their changes to a live server, or when you don't have access to the server at all. And dare I say, script kiddies and hackers will definitely have a ball!
It works by sniffing what browsers are looking for, and by using your rules it can figure out whether you wish to server a different file, such as a file on a completely different server, Or a file on your desktop! What’s amazing though, is the website still thinks it is from the URI it was originally accessed. Meaning you do not get XSS problems.
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