The Unified Modeling Language (UML) is an industrial standard for object-oriented software specification, which offers notational conventions for system modelling at the initial stage of software development. Despite the number of different approaches to development of UML class diagram based on formal transformations of its elements from the problem domain, still there is no widespread tool available for automatic generation of UML class diagram from some form of the problem domain description. Four components form the architecture required for development of such a tool, namely, the drawing environment for source model, export of source elements for their transformation to target, definition of transformation rules themselves, import of the target model into some UML-compatible modelling environment. The paper presents the process of how BrainTool was developed by a research group in Riga Technical University and how it generates the UML class diagram from the two-hemisphere model. Authors of the paper share their experience on the selection of technical solutions for BrainTool implementation and mention several lessons learned during the development process.