Great web dev tool: Microsoft Fiddler

Microsoft Fiddler is an HTTP debugging proxy. It allows you to see the contents of HTTP requests as well as alter them on the fly using Javascript. You can download it from here and read about it on MSDN.

It works fine with Firefox but if you are prepared to use IE then it's more transparent because when you start it up it reads your system proxy settings and configures itself using them, and then replaces the system proxy settings with itself.

Once configured you get to watch requests in much the same way as with the Eclipse Proxy Tool that comes with WTP.

Fiddler however also allows you to alter the HTTP requests on the fly, or reply them, or script changes using Javascript (sorry JScript.NET).

It is a useful AJAX debugging tool because it captures all your Ajaxian requests and it is nice (and slightly scarey) to see all the requests made by apps that send background requests to auto-update and so on.


Raffaele P.Guidi Re: Great web dev tool: Microsoft Fiddler

Try also webScarab, wich handles http, https, cascading proxies. It is pure java, released under the GPL, comes with a plugin architecture and many plugins (such as a BeanShell one).

Re: Great web dev tool: Microsoft Fiddler

You can use the Tamper Data plugin with Firefox ( Some screenshots:

Re: Great web dev tool: Microsoft Fiddler

If you're interested in XMLHttpRequest traffic specifically and you're a Firefox user, you should check out this XMLHttpRequest Debugging tool:

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