In the last years we applied the Method Engineering paradigm to the development of agent-oriented design processes. The main difficulty in our initial experiments was ensuring the support of a customised CASE tool to the new methodology. In this paper we now present a Computer-Aided Process Engineering (CAPE) tool that we developed in order to allow the design of the new process and then its instantiation. The process is executed as a workflow, the designer receives the help of an expert system (for routine works automation and syntax/semantic checks) and can model his/her system using a set of Eclipse plug-ins supporting all UML diagrams. The development of this tool started from the definition of a system metamodel obtained from the initial requirements and then instantiated using open-source and ad hoc developed components; as it could be expected relevant portions of this tool are developed using the agent-oriented paradigm.