User interface testing is a very important but time consuming activity. To automate and systematize the testing process, models can be used to derive test cases automatically -a technique known as model-based testing. Given a model representing the intended system behavior and a test suite derived from the model or produced manually, the coverage of the test suite over the model is an important early indicator of the quality and completeness of the test suite. This paper presents a novel tool that shows visually the coverage achieved by a test suite over an UML model of an interactive system. This model is based on activity and class diagrams, with special user interface modeling features (stereotypes and keywords) inspired in ConcurTaskTrees and Canonical Abstract Prototypes. The tool receives a UML model file and a test suite, determines the model coverage by simulating the execution of the test suite over the model, and produces a colored UML model showing the elements covered. An example is presented to illustrate the approach.