Abstract: Systems and methods for predicting the viability of producing target molecules in a host organism are provided. A starting metabolite set for the host and a reaction set are obtained. Included in a filtered reaction set are reactions that are indicated as catalyzed by one or more corresponding catalysts that are themselves indicated as likely available to catalyze the reactions in the host organism. In each processing step, pursuant to the reactions of the filtered reaction set, data representing the starting metabolites and metabolites generated in previous processing steps is processed, to generate data representing one or more viable target molecules.