Plugin Consultant is a VST Plugin created by Ofer Shem Tov. I'm hosting it here, since his web got lost; currently, this is PlugIn Consultant V1.1, which has been done for VST SDK 2.3. I'll update it to use the VST SDK 2.4 sometime soon.

Here's Ofer's original text:

Plugin Consultant

Free, Open Source, Cross Platform, VST API Monitoring and Logging Tool

Plugin Consultant makes it easier for VST plugin and host developers to debug their products and for new developers to learn how the VST API works.

With Plugin Consultant you can monitor and log VST API calls between your plugin and any host, between your host and any plugin or between any plugin and any host.

Plugin Consultant provides clear view of all communications between VST plugins and hosts:

	Shows what functions and opcodes are called and how often.
	Provides control of what functions and opcodes are logged and with what details.
	Generates detailed log, using standard Win32 OutputDebugString, can be viewed in your debugger or in any debug viewer.
	Does not change plugin or host behavior.
	Does not require the logged plugin or host to be compiled in Debug mode.
	Can log plugins and hosts written in any language (the VST C API is logged), including plugins created with SynthEdit.
	Can log plugins and hosts that will not agree to run under a debugger.
	Works with plugins and hosts that use VST SDK version 2.3 or earlier.

Additional Downloads:

plugin_consultant_guide.pdf (Documentation, 261 KB)