Software architecture, and its behavior can be expressed as UML models. Models of complex systems can be also complex and hard to read – they may consists of hundreds of artifacts. Analysis of such complicated models is very difficult. Applying design guidelines make this process easier. Design guidelines consist of some rules, and constraints that should be applied during models construction. They increase readability of models, and in consequence assure higher quality of the final product. The paper presents Model Verificator – the tool for checking UML models against a given design standard. The tool works as a plug-in to Rational Rose. The guidelines take the form of XML file compliant with some DTD. Verification is done fully automatically. The tool also enables correction of checked models.