ComTrace

ComTrace is a tool that will intercept both calls made on your interfaces and calls made to the COM library, and trace these for you. You will see the name of the method call, the parameters passed to the method and the returning HRESULT.

Interface definitions

In order to trace calls on any interface, ComTrace needs to know the signature of the interface. Interfaces that has a corresponding typelibrary will be traced automatic since ComTrace can load the typelibrary at runtime to learn the signature of the interface. For interfaces that doesn't has a typelibrary (such as custom interfaces), ComTrace has a directory from where it parses IDL files to learn interface signatures. If your interfaces don't have a installed typelibrary, you can copy your IDL files into the \IDL directory (for instance C:\Program Files\ComTrace\IDL).

Screenshots

For an screenshot on ComTrace in action, see this image and this one.

Download

A free download for Windows XP here: ComTraceSetup.exe. I'm sorry to write that I have no plans on updating with support for Vista and 7 (unless I somehow find enough time to do so).