SiMRX is a MRX simulation toolbox written in MATLAB for simulation of realistic 2D and 3D Magnetorelaxometry (MRX) setups, including coils, sensors and activation patterns. MRX is a new modality that uses magnetic nanoparticles (MNP) as contrast agent and shows promising results in medical applications, e.g. cancer treatment. Its basic principles were outlined in [Baumgarten et al., 2008], further elaborated in [Liebl et al., 2014], transferred into a rigorous mathematical model and analyzed in [Föcke et al., 2018].