In this paper, we introduce the WorkSim model, a novel agent-based framework to study labor markets. The first objective of the model is to reproduce the gross flows between the important states: employment (distinguishing fixed term contracts and open ended contracts), unemployment and inactivity, and the ratios of individuals in these states. The novelty of the model is that it simulates the flows on the basis of the rational decisions of individual heterogeneous agents. Once the model is calibrated, the second objective is to characterize the nature of the labor market under study. This is done, first by examining the patterns of flows and stocks at the aggregate level and at the levels of different categories of labor, and second by sensitivity experiments, modifying some exogenous parameters and variables such as the demand for the good. Finally the model once calibrated is a tool for experimenting labor market policies, including changes in the labor law in France.