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:
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:
plugin_consultant_guide.pdf (Documentation, 261 KB)
Copyright 2005 By Ofer Shem Tov