cctbx.xfel is a suite of software tools designed to process diffraction data from serial femtosecond crystallography (SFX) measurements at an X-ray free-electron laser (XFEL) or a synchrotron. Built on the Computational Crystallographic Toolbox (cctbx), the same toolbox on which Phenix, DIALS, LABELIT, and post-refinement and merging program, PRIME are built, it enables the user to solve difficult problems relating to processing serial crystallographic data. The programs and modules provided by cctbx.xfel can reduce a large set of still diffraction images recorded at Stanford’s Linac Coherent Light Source (LCLS), SACLA, the European XFEL, or a synchrotron, to a single MTZ file containing merged reflection intensities suitable for structure solution.