How to make Roslyn Syntax Visualizer Extension work?

The Syntax Visualizer only works when you are running Visual Studio with Roslyn enabled. When you start a test instance of Visual Studio, Roslyn is automatically enabled. Manually starting Visual Studio with Roslyn can be done by adding /rootsuffix Roslyn to the shortcut, but take care that Roslyn is not finished yet. It might not be advisable to enable it by default, depending on what you are working on. Of course, you can also just create another shortcut with Roslyn, so you can choose which one you want.

If you see [Roslyn] in your code tabs in Visual Studio, then you can use the visualizer. Another way of verifying if Roslyn is enabled is to view your extensions. The Roslyn Language Services has to be there for it to work. If this is not the case, then the visualizer can be opened, but it won't show any contents.

You can find more information about the visualizer extension here.