Instead, BespokeFit groups the torsion parameters using symmetry labels as defined by the bonding topology of the molecule. In the case of the highlighted rotatable bond in aspirin, two unique torsions (9-8-11-6 and 9-8-11-12) are identified due to the terminal atoms (labelled 6 and 12) having different local environments (Figure (left)). As SMIRKS patterns can be more expressive than the combination of predefined atom types, we can create a single bespoke pattern that matches all of the torsions with identical symmetry labels (as determined by RDKit or the OpenEye toolkit ). This allows BespokeFit to automatically introduce extra parameter flexibility via the splitting of torsion parameters into unique symmetry types, which has been shown to be essential for accurate reproduction of reference potential energy surfaces . Conversely, a similar analysis is shown in Figure for biphenyl, where symmetry labels avoid the unnecessary splitting into separate torsion types and simplify the parameter optimization step. Thus, the use of symmetry labels and SMIRKS patterns in BespokeFit provides an automated means to optimally select torsion types for fitting.