The researches of generative models for molecules in the early days were mainly focused to increase the ratio of valid molecules among all generated ones. RDKit has been used to assess validity , and validity is now regarded as one of the most important benchmarks for evaluating generative models . After numerous efforts on increasing the validity ratio, the generative models in the most recent reports succeeded in achieving very high validity. However, it has been pointed out that such benchmark metrics including validity cannot properly evaluate the generated molecules. Renz and coworkers showed failure mechanisms of generative models. In the work, they exemplified the generated molecules could contain unstable, synthetically infeasible, or highly uncommon substructures . In Figure , examples of such unwanted molecules are shown.