We present an open-source * rapid simulator for species concentrations in channel-based microfluidic networks to accelerate the simulation step in the design cycle for microfluidic devices.The concentration of species is important in many microfluidic devices, and simulating it is an important step in their design cycle.Simulating concentrations is usually done using Computational Fluid Dynamics (CFD) methods, which are costly and time-consuming, especially for large microfluidic networks.Here, we present an open-source abstract simulator for concentrations in microfluidic devices that rapidly provides reliable results [1].With this simulator, the (automatic) design and validation of larger microfluidic devices becomes feasible.