Purpose of SimEx SimEx is a python library to facilitate setup, execution, and analysis of simulations of experiments at advanced laser light sources. As an example, consider a molecule radiated by highly brilliant, ultrashort x-ray pulses such as delivered by an X-Ray Free Electron Laser (X-FEL). The simulation platform allows to combine tools and codes for the simulation of each step of the experiment: Generation of radiation in the photon source, propagation through optics and waveguides to the interaction point, photon-matter interaction, scattering of the radiation into the far field and detection of the latter. The platform provides slots and interfaces for the various simulation steps. Repository: https://github.com/PaNOSC-ViNYL/SimEx This release on GitHub: https://github.com/PaNOSC-ViNYL/SimEx/releases/tag/v0.5.0 This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654220 and No 823852.