Simulation can be an important conceptual and practical tool to support the engineering of multi-agent systems (MAS), in different ways. In this paper we consider the case in which simulation is applied and exploited directly upon a MAS developed using an existing agent/MAS programming platform. That is: without requiring to model and simulate agents and their environment using a different platform, e.g. an agent-based simulation one. In particular, we describe the design of JaCaMo-sim, an extension of the JaCaMo platform that makes it possible to both run and simulate the execution of MAS programs based on BDI agents written in Jason, situated in artifact-based environments developed in CArtAgO. The tool can be useful for different aspects that concern MAS engineering, from MAS testing/debugging at development time to agent decision making support at runtime.