Open-source interface to Bird’s DSMC code for complex interaction. A plug-in-based interface to the 2D Direct Simulation Monte Carlo (DSMC) programme DS2 written by G.A. Bird is proposed. The interface enables the user to read and modify certain variables and data structures inside the simulation at runtime. With this tool, the user can apply the DSMC method to custom problems and rely on a mature DSMC code. Some of the most interesting data structures are the surface properties like adsorption coefficients, reaction probabilities and temperature and the properties of the inlet streams. All those quantities can now be altered at runtime within the DS2 programme with the proposed interface. The various features of the plug-in and the coupling between them are demonstrated using four exemplary geometries.