Snoop is the open source WPF spying utility created by Pete Blois and now maintained by Team Snoop (Cory Plotts, Dan Hanan, Andrei Kashcha, and Maciek Rakowski).

It allows you to spy/browse the visual tree of a running application (without the need for a debugger) … and change properties ... amongst other things.

The most recent version of Snoop, Snoop 2.7.1, was released on May 4th, 2012. Go to one of download pages (CodePlex or GitHub) to download it.

The Snoop repository has been converted to Git and is now being hosted in two public repositories (which will be kept in sync), the one at CodePlex (http://snoopwpf.codeplex.com/) and the one at GitHub (https://github.com/cplotts/snoopwpf). See the 2.7.1 release notes for more info.

I have copied the documentation from Pete Blois’ Snoop page to the Documentation area on CodePlex. It is quite out of date (obviously). Some day, I hope to update it with current screen shots and information.

I also have a blog series on Snoop Tips & Tricks. Here is a link to the first one (from where you can get to the others as they appear).

One question that comes up all the time is the situation where the application you are trying to Snoop, isn't appearing in the application chooser (i.e. the  combo box that lists the processes you can Snoop). This is more than likely a situation where the application you are trying to Snoop is running elevated (as Administrator). In order to Snoop these applications, you will also need to run Snoop elevated (as Administrator).

Snoop is not currently able to spy Silverlight applications (maybe some day). In the meantime, if you want to do that, I would point you to Koen Zwikstra's awesome utility, Silverlight Spy.