Web Services were designed for Enterprise systems. They are a flexible but complex technology, with numerous performance pitfalls for developers. They also have significant overhead when compared with platform-specific solutions (e.g. Java RMI). The end solutions have to combine (virtualized) platform, application framework, and application-specific code. As a result of this complexity, the performance of the final application is often disappointing and requires improvement. This paper describes the implementation of performance tools for an open-source application framework based on the Java platform and presents the findings of a detailed assessment of Web Services performance using the newly developed tools. The challenges, techniques, and lessons learned are relevant beyond the scope of the used framework because widely used open-source libraries were studied as well, namely: Hibernate, JAX-WS, and Log4J. 10 http://groovy.codehaus.org/