Active-Filtering of the Session List in Fiddler2

I use Fiddler2 daily – it’s one of the greatest debugging tools I’ve ever come across. You can hammer into the traffic coming and going across the tubes and tamper with the data as you like. You can substitute alternative local data in the place of remote server responses. You can modify headers on the fly. And this doesn’t even begin to scratch the surface of all you can do.

One of the problems I have is that, like many of you I’m sure, my browser is hardly ever doing one thing. Although I may be trying to debug a web-app, I may also be tied into my GMail inbox, streaming some music over Turntable, or watching the flow of tweets glide across @jonathansampson. All of these items cause sessions to be logged in Fiddler, adding a whole lot of noise to what I’m trying to work on.

So what do you do when you have specific hosts that you want to track? You make use of the Filters tab.

This highly-customizable tab will provide active filtering of the sessions coming across your screen. You can instruct it to show only intranet traffic, or only internet traffic. You can explicitly ignore particular hosts, or you can ignore everything but a select few. As my earlier summary of Fiddler didn’t begin to scratch the surface, neither does my explanation of this panel begin to touch on all that the Filter feature is capable of.

Have a look.

What I’ll be looking at here is the first part, the hosts section.

For starters, we need to click the “Use Filters” check-box to enable this feature. Now in my particular situtation all I want to see is anything that comes from a particular domain, such as This would include any subdomains as well.

The first thing I will do is select “Show only Internet Hosts” from the first dropdown. From the second dropdown, I’ll select “Show only the following Hosts”. This enables the textarea below, which will take a series of expressions or explicit domains to watch for.

Insert * and you should see the textarea turn yellow, informing us that “Changes not yet saved.” At this point, click the Actions button to the top-right, and select “Run Filterset now”. If you already had sessions from your target domain in your session list, those should be all you see in there at this point.

From this you can infer how to go about blocking only particular domains, and various other things. You might even dare to venture into the rest of the filter options, creating a highly-customized instruction set. If you do, be sure to save your filter from the same Actions button we used to run the filterset.

I find this to be an enormously helpful feature, and I’m sure you will as well. Now if you’ll excuse me, I’ve got some work to do and very little noise preventing me from getting it done, thanks to Fiddler.