SMARTS patterns are search queries on molecules that identify specific molecular substructures. Here, we call these specific substructures "chemical environments." SMARTS can easily be written by hand, yet are expressive enough to pinpoint specific molecular details. Given a set of SMARTS patterns, it is possible to group chemical environments together in a way that resembles a clustering scheme. In general, SMARTS-based clustering is a data labeling operation where chemical environments that match to some SMARTS share the same label. We are interested in the case of force fields for molecular dynamics, where the labels are atom types.