JSXM: A Tool for Automated Test Generation. The Stream X-machine (SXM) is an intuitive and powerful modelling formalism that extends finite state machines with a memory (data) structure and function-labelled transitions. One of the main strengths of the SXM is its associated testing strategy: this guarantees that, under well defined conditions, all functional inconsistencies between the system under test and the model are revealed. Unfortunately, despite the evident strength of SXM based testing, no tool that convincingly implements this strategy exists. This paper presents such a tool, called JSXM. The JSXM tool supports the animation of SXM models for the purpose of model validation, the automatic generation of abstract test cases from SXM specifications and the transformation of abstract test cases into concrete test cases in the implementation language of the system under test. A special characteristic of the modelling language and of the tool is that it supports the specifications of flat SXM models as well as the integration of interacting SXM models.