The Open Force Field toolkit provides an alternative approach to traditional atom type assignment through "direct chemical perception," which assigns force field parameters through SMIRKS Native Open Force Field (SMIRNOFF) chemical environment queries directly on the molecular graph (Figure ). In this way, local chemical environments with distinct bond interaction types, neighbors, and charges are captured in a condensed format that allows for a more extensible encoding of traditional atom types. Figure : Visual description of the SMIRKS chemical query language used to find substructure matches (color-coded) for bond parameters between atoms 1 (yellow) and 2 (blue). Reproduced from Mobley et al. SMIRNOFF encoding greatly reduces the complexity of the parameterization process and allows for the simulation of highly diverse chemistries with the definition of additional bonded types. Recent OpenFF efforts have produced the Sage 2.0.0 force field with comparable performance to other small molecule force fields such the General Amber Force Field (GAFF) while also containing all necessary chemical query information and parameters within a 400 line file. Additionally, Open Force Field provides an open-source implementation of the SMIRNOFF specification available for download and use. Although the OpenFF line of force fields is designed for small molecules, the SMIRNOFF query format is powerful enough to generalize to many classes of molecular dynamics applications, assuming that a chemical topology is provided with all chemical information.