A new software package, DISTL (Diffraction Image Screening Tool and Library), for the rapid analysis of X-ray diffraction patterns collected from macromolecular crystals is presented. Within seconds, the program characterizes the strength and quality of the Bragg spots, determines the limiting resolution of the image, and identifies deleterious features such as ice-rings and intense salt reflections. The procedure also generates a reliable set of intense peaks for auto-indexing. The ability to classify a large number of crystals quickly will be especially useful at synchrotron and home-laboratory X-ray sources where automated crystal screening and data collection systems have been implemented.