How does the substructure search work in the CSD web interface (SMARTS)?

The substructure search in the CSD web interface uses the sketcher to create a query in SMARTS format that is then used to search the CSD. This SMARTS format (SMiles ARbitrary Target Specification) is simply a language for describing substructures in molecules that can be represented as a simple string of ASCII characters. Users do not need to understand SMARTS to use this search interface, but you can see the SMARTS pattern produced by the sketcher for your substructure as the query is run in WebCSD. If you would like to learn more about SMARTS or visualise SMARTS patterns, the web application SMARTSviewer by the University of Hamburg is an excellent reference.