Most of the FDA-approved drugs are known to be metabolized by a ubiquitous protein family of heme-thiolate enzymes known as cytochrome P450s (CYPs). Regioselectivity-WebPredictor (http://reccr.chem.rpi.edu/Software/RS-WebPredicto/) is an algorithm for accurate prediction of isozyme-specific cytochrome P450 (CYP)-mediated sites of metabolism (SOM) on drug like molecules (Nebert & Russell, 2002). This is the very first repository that makes metabolic predictions for nine isozymes (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4) available to the public and uses models trained on the largest set of CYP substrate and metabolite data (Zaretzki et al., 2013).