XAML Spy is Now Free
First Floor Software, makers of XAML Spy, is now offering a free version of their flagship product. Known as XAML Spy Express, this product allows developers to browse the visual tree of a running application. Unlike its open source competitor, Snoop, XAML Spy supports Silverlight, Windows Store, and Windows Phone in addition to WPF. Note that examining Silverlight 3/4 apps requires having Silverlight 5 installed.
XAML Spy also offers a commercial version. That version adds the ability to edit properties much like a web browser’s built-in HTML/CSS debugger. It can also serialize a control back to the XAML that represents its current state.
Both the free and commercial version of XAML Spy 2 are integrated into Visual Studio. XAML debugging is enabled simply by right-clicking on the project file. There is, however, a performance hit from this so they provide a way to easily disable it as well. And by default it is limited to debug builds only.
If you prefer to use a stand-alone XAML debugger, XAML Spy 1 is still available. This can be installed side-by-side with XAML Spy 2 and allows developers to attach to any running WPF application. An internal web browser is used for debugging Silverlight applications. In a future update XAML Spy 2 is expected to regain the ability to run outside of Visual Studio.
XAML Spy relies on what they call the XAML Spy service. Running applications and debuggers communicate with each other via this service. Unfortunately firewalls and VPN connections can interfere with this service, sometimes even after the VPN connection is dropped.