ESPsim is a small RDKit/NumPy/SciPy package that scores how similar two small molecules are in ELECTROSTATIC POTENTIAL and in SHAPE. It computes the overlap integral of the two molecules' electrostatic potentials (analytically, by fitting the 1/r Coulomb term with three Gaussians, or numerically by Monte-Carlo integration), turns it into a Carbo or Tanimoto similarity, and pairs it with RDKit's shape Tanimoto. It also ships helpers to embed (generate 3D coordinates for) molecules against a constrained 3D core and to align-and-score a probe molecule against a set of references.