Prototyping object oriented specifications CoopnBuilder is an integrated development environment (IDE) for Concurrent Object Oriented Petri Nets (COOPN). It comes with a complete set of tools enabling the user to view, edit, check, simulate and generate code from CO-OPN specifications. The Code Generation tool allows the user to develop applications in an open way: the produced code can be integrated in larger projects or use existing libraries. The code generation will be emphasized in this paper, and we will focus on ease-of-use and extensibility. CoopnBuilder is an open-source Java program and can be downloaded from url{}.