FxCop rules can be debugged using the debugger that is built in to Visual Studio. The key to debugging rules is to understand that you need to run the FxCop GUI application in the debugger since that application in turn loads your rules assembly. There are two basic ways to perform the debugging: by attaching to a running FxCop executable or by starting FxCop directly from your Visual Studio project.

To attach to a running FxCop executable, start FxCop normally. Next, ensure that your rules project is open in Visual Studio. Click the Tools, Attach to Process... menu item. Highlight the FxCop.exe process and click Attach. Now, perform an analysis using FxCop. Any breakpoints that you have set in your code will step into the debugger as they are encountered.

Alternatively, you can configure your rules class library project to start FxCop for debugging whenever you use Visual Studio to run your project (for example, by clicking the Run toolbar button or pressing the F5 key.) Click the Project, <projectname> Properties menu item. Go to the Debug page. Choose Start external program and enter the path and filename for the FxCop program, such as C:\Program Files\Microsoft FxCop 1.36\FxCop.exe.