Yasper: a tool for workflow modeling and analysis. This paper presents Yasper, a tool for modeling, analyzing and simulating workflow systems, based on Petri nets. Yasper puts Petri net modeling in the hands of business analysts and software architecture designers. They can specify systems in familiar terms (XOR choice, workflow, cases, roles, processing time and cost), and can directly run manual and automatic simulations on the resulting models to analyze correctness and performance. Yasper was designed to cooperate with other tools, such as Petri net analyzers, and off-the-shelf software for data (color) handling and forms handling.