This paper presents J-MADeM, a new market-based multi-agent approach devoted to perform social simulations with BDI agents. J-MADeM is available as an open-source library integrated into Jason [2], the successful interpreter for the AgentSpeak programming language [16]. The aim of this work is to improve Jason by incorporating the main features of MADeM [10], a market-based mechanism for social decision making. Thus, J-MADeM agents can easily define the utility functions expressing their preferences and find socially acceptable decisions for specific decision problems. This paper fully explains the three main features offered by J-MADeM to AgentSpeak programmers: (i) an agent architecture that Jason agents can use to carry out their own MADeM decisions, (ii) an interface to develop utility functions that can be used along with the MADeM model and (iii) a set of internal actions to manage the parameters of these kinds of decisions.