Using ECA rules in active database systems for real-life applications involves implementing, debugging, and maintaining large numbers of rules. Experience in developing large production rule systems has amply demonstrated the need for understanding the behavior of rules especially when their execution is non-deterministic. Availability of rules in active database systems and their semantics creates additional complexity for both modeling and verfying the correctness of such systems. As part of sentinel-an object-oriented active DBMS, we have developed a visualization tool to help understand the behavior of rules defined as part of an active database application. This is especially important in active databases as rules are invoked (as a side effect) based on event occurerrences (both primitive and composite) and are executed concurrently based on user-provided priority information. In this paper, we describe the rationale: for the development of the tool, how it has been implemented exploiting the architecture of sentinel, functionality of the esulting tool, and show several screen dumps to provide a feel for the information presented by the visualization tool.