In this paper we introduce GOAD – an active database we have developed on top of GemStone – concentrating upon the implementation of our debugger prototype. We show how we extended the standard debugger provided with the GemStone-Smalltalk Interface to cope with the added complexity which the active parts of our system present. These extensions provide the means to trace the execution of rule code in the same straight-forward manner as standard class code. In addition we show how the GOAD visibility-toggling mechanismcan be used by the debugger to provide different representations of an active application which are tailored to the needs of different types of users. We give an example of how, in conjunction with more abstract, graphical tools, we can use our debugger to help deal with errors in the functioning of the rule base. We conclude by evaluating the usefulness of our tool and the suitability of Smalltalk and GemStone as an underlying system for the development of tools such as the one we describe.