We consider a tool requirements planning problem (TRPP) of determining the number of tool copies for each tool type in a flexible manufacturing system with an automatic tool transporter. In this paper, four heuristic algorithms are developed for the TRPP with the objective of minimizing the total tool purchase cost subject to a makespan constraint. In the algorithms, starting from an initial (infeasible) solution, the numbers of tool copies for certain tool types are increased at each iteration until the makespan constraint becomes satisfied. In these algorithms, information obtained from discrete event simulation is used to select tool types of which the numbers of copies are to be increased. Computational experiments are performed on randomly generated test problems and results show that good tool requirements plans can be obtained with the heuristic algorithms in a reasonable amount of computation time.