dnSpy is a debugger and .NET assembly editor. You can use it to edit and debug assemblies even if you don't have any source code available.
Some Features
- Debug .NET Framework, .NET Core and Unity game assemblies, no source code required
- Set breakpoints and step into any assembly
- Locals, watch, autos windows
- All metadata can be edited
- Edit methods and classes in C# or Visual Basic with IntelliSense, no source code required
- Add new methods, classes or members in C# or Visual Basic
- IL editor for low level IL method body editing