The impurity ranking portion of the workflow consists of steps 12, 13 and 14 in Figure , and aims to rank suggested impurities considering reaction conditions, relevance scores and number of hits. Step 12 involves calculating Morgan fingerprint similarities between analogue and query species in suggested impurity reactions. This is based on the understanding that the most relevant analogue reactions will contain analogue species that not only consist of common reacting carrier fragments respective to query species but are also highly similar when comparing overall respective molecular structures. Fingerprints can capture a wider molecular context, at the expense of interpretability. In particular, ECFP (Extended Connectivity Fingerprints) or Morgan fingerprints encode heavy atoms in circular layers up to a specified diameter, and are widely employed. In this case, for each analogue reaction, 1024-bit ECFP4 fingerprints (radius of 2) were used to characterize molecules, and dice similarities were computed between analogue reactants, reagents and respective query species in the suggested impurity reaction using bespoke RDKit functions. These similarities were averaged, with the final value reflecting the relevance of the analogue reaction with respect to each suggested impurity reaction, as shown in Figure .