The Rigaku PlateMate is a tool that allows one to mount SBS format crystallization plates on Rigaku goniometers for in situ diffraction experiments. Protein crystallography often requires screening large numbers of crystals to identify samples suitable for X-ray data collection. Traditionally, crystallographers mounted crystalline samples in capillaries — a time consuming task often resulting in damaged crystals — to evaluate sample quality prior to cryo-freezing. The PlateMate, a tool originally designed by crystallographers at AstraZeneca and adapted by Rigaku, streamlines the screening process because it eliminates the need to harvest crystals from crystallization plates. Instead, crystals can be evaluated in situ, using existing X-ray diffraction equipment, to determine whether they are composed of protein or salt and to evaluate diffraction resolution, mosaicity and other crystal parameters. Thus, the PlateMate is a low-invasive, fast tool for benchmarking diffraction quality prior to sample harvesting and freezing.