We developed an impurity predictor based on SMARTS reaction templates, describing how the products in a chemical reaction are formed by combining fragments of the starting materials (Figure ). We integrated data from an internal electronic laboratory notebook reporting performed reactions with the corresponding starting materials and analytically detected impurities (Figure ) allowing us to cover both the desired reactions forming the main compound and additional processes that generated detected impurities. By codifying an asset's synthesis route as a sequence of template applications we were able to generate a dataset of impurities that is entirely simulated from first principles only based on the knowledge of the synthesis route (Figure ).