of transformation-based fragment-based libraries. In the field of fragment screening, more than twenty years ago Congreve et al. proposed a set of empirical rules known as the rule of three (RO3, MW < 300, cLogP ≤ 3, HBD ≤ 3, HBA ≤ 3). Although the RO3 has limitations, the concept has given relevant resources in FBDD, especially limiting the molecular complexity of fragments libraries, giving place to an adequate exploration of diverse zones of the molecular space, and avoiding 'molecular obesity'. Currently, there are multiple commercial or free accessible fragment libraries, much of them based on small synthetically accessible molecules, focused on particular biological activities, among others.