MARXS (Multi-Architecture-Raytrace-Xraymission-Simulator) is a toolsuite to simulate the performance X-ray observatories. It is primarily aimed at astronomical X-ray satellites and sounding rocket payloads, but can be used to ray-trace experiments in the laboratory as well. MARXS performs Monte-Carlo ray-trace simulations from a source (astronomical or lab) through a collection of optical elements such as mirrors, baffles, and gratings to a detector.