Japex is a simple yet powerful tool to write Java-based micro-benchmarks. It started as a simple project over a year ago, primarily aimed at testing XML and Fast Infoset performance, but has evolved into a rather sophisticated framework with support for XML and HTML output as well as various types of charts for displaying the results. It is similar in spirit to JUnit in that if factors out most of the repetitive programming logic that is necessary to write micro-benchmarks. This logic includes loading and initializing multiple drivers, warming up the VM, forking multiple threads, timing the inner loop, etc. One of the key design goals for Japex was extensibility. Via the use of a simple model of input and output parameters, it is possible to write micro-benchmarks to test practically anything.