The Unified Modeling Language, has become effectively the standard modeling language for analysis and design of software systems. However, despite achievements in defining semi-formal semantics, with a combination of OCL constraints and textual descriptions of the UML semantics, UML is still an informal language. This paper introduces a tool for developing correct models of distributed and reactive systems using UML and Rebeca. Rebeca is an actorbased modeling language supported by a formal verification tool. This approach can bridge the gap between software development and formal verification by allowing users to develop their systems using UML and yet getting advantage of formal verification support of Rebeca tools and theory. In this way, we combine two separate approaches to modeling by adding verification step to software development lifecycle. Furthermore, this can make a contribution to defining rigorous semantics for UML diagrams and to provide tool support for verification of these diagrams.