The Zope component registry is a black box in normal operation. Requests are made of the registry for components appropriate to the request and it returns them. If something goes wrong, it raises ComponentLookupError. This is very much as it should be since the inner workings of the registry should no more be apart of application design than should the inner workings of Python.
In the process, however, of developing an application that uses the registry, it is often desirable to have more introspection of the registry available.
z3c.componentdebug provides a set of tools for inspecting the component registry of site managers. It also provides a patch that catches various different ComponentLookupError exceptions and adds more verbose reporting.