In the normalization process, one of the key transformations/adjustments applied to the molecular structure is tautomer enumeration. Tautomers are constitutional isomers of organic compounds that interconvert by chemical reactions, most often involving the transfer of one or more hydrogen atoms between different heavy atom centers (prototropic tautomerism). The InChI normalization algorithm involves enumerating tautomeric forms and selecting the most appropriate representation based on established rules and guidelines. This ensures that the resulting InChI represents the most stable and chemically relevant tautomeric form.The standard InChI supports only limited tautomerisms, however, additional tautomerisms are available in the engineering mode. By applying this normalization transformation, the InChI ensures that diverse molecular structures are represented in a reproducible and consistent manner, thereby facilitating accurate interpretation and comparison across different chemical compounds.