Fragmenstein is open source. The open-source codebase for Fragmenstein can be found at . Code and data for benchmarks (vide infra) available at manuscript-data. Fragmenstein merges or places compounds by stitching together the atoms of the hits. Fragmenstein has two main functionalities (Figure ): fragment hit combination and derivative placement, both constrained by the fragment hits that inspired them. Both these operations require two steps: (i) the creation of a potentially distorted compound whose atoms overlap the parent hits and (ii) the energy minimisation of the compound under strong constraints. The two functionalities can be used as a single continuous workflow (viz. GitHub repository). First, fragments are combined (merged/linked) with Fragmenstein, then a search is conducted via the SmallWorld server () for purchasable analogues in Enamine REAL or equivalent supplier (i.e. analogue-bycatalogue), and lastly candidate compounds are placed with Fragmenstein in order to be ranked. The operations performed are described in the GitHub repository and outlined in Figure .