xmm_simulator generates mock XMM-Newton images and spectra from 3D galaxy cluster simulations from hydrodynamical simulations. It generates particle background spectra from filter-wheel-closed data, a realistic sky background model, energy-dependent vignetting, energy redistribution, and PSF convolution. Users can extract lists of simulated events, corresponding photon images, exposure maps, non-X-ray background maps, and spectra with redistribution matrices and weighted ancillary responses. xmm_simulator also includes tools to sum maps from multiple instruments and to organize simulation outputs into FITS files suitable for further analysis.