ClusterCAD provides a database and web-based toolkit designed to enable researchers to harness the potential of type I modular polyketide synthases and nonribosomal peptide synthetases for combinatorial biosynthesis. We provide tools to identify a truncated PKS or NRPS as a starting point for domain exchange experiments given a small molecule target, and to select subunits as catalytic domain donors to alter a module’s acyltransferase, ketoreductase, or reductive cassette. View the video below for a quick tutorial. Please cite us if you use ClusterCAD for published research.