The OpenChemLib substructure search provides a number of mechanisms to perform advanced substructure search that goes beyond searching for a specific subgraph. These mechanisms are provided via so called query features. There exist broadening (i.e. relaxing) query features on bonds and atoms, as well as narrowing (i.e. constraining) query features on bonds and atoms. Broadening query features include the possibility to match bonds of the query structure to different bond types, or to match atoms of the query structure to multiple atom