Object-oriented system modeling enables the sharing of responsibilities between system objects at a high level of system abstraction. The UML class diagram is the central part of the object-oriented system model and serves as a "bridge" between the information about the problem domain at the customer's side and the software components at the developer's side. However, UML is not a methodology for how to model the system, but just a notation for "drawing" of model elements. This paper demonstrates the functionality of the BrainTool, which enables the generation of the UML class diagram from the so called two-hemisphere model, where the problem domain is presented as a concatenation of the problem domain processes, incoming and outgoing information flows and their types. BrainTool is developed using Visual Studio .NET for modeling of the two-hemisphere model, the Python programming language for definition of transformation rules and XMI for model interchange with Sparx Enterprise Architect.