The PlateMate is a simple, inexpensive tool for rapid screening of crystals within crystallization plates. The PlateMate is equipped with a standard IUCr fitting for easy installation on most Rigaku Oxford Diffraction goniometers, and supports SBS format crystallization plates. With the PlateMate, you can easily answer the questions: “Is it a protein crystal or a salt crystal?” and “How far does my crystal diffract at room temperature, prior to cryofreezing?” In addition, the PlateMate enables you to collect complete, or nearly complete, data sets for many protein crystals without ever removing the crystal from the crystallization drop. The PlateMate also provides an important time gain for fragment screening projects and for screening crystals for bound compounds in protein active sites. Herein, we describe a data collection example using the PlateMate.