How do I Debug a SingleFileGenerator/ Custom Tool?

I am building a Custom Tool code generator using the Visual Studio SDK and basing it on the SingleFileGenerator example.

My question is how to enter debug mode on this code? I can currently add my custom tool to a file in Visual Studio but it errors out, I'd like to be able to debug this code if possible.

From stackoverflow

• You need to debug Visual Studio, you can either do it by attaching to a running session (Tools\Attach To Process) or by setting Visual Studio (devenv.exe) to be your startup project of the Custom Tool Project.