Both physics-based electronic descriptors and structure-based steric descriptors are used in Reaxtica. To simplify the calculation of QM-based descriptors, we make use of a GNN-based descriptor predictor known as qmdesc to generate Hirshfeld partial charges, nucleophilic Fukui indices, electrophilic Fukui indices, NMR shielding constants, bond lengths, and bond orders with DFT-level precision. It should be noted that the former four descriptors are atom-based while the latter two are bond-based descriptors. In addition, TSEI and Sterimol 30 are used to reflect the structure-based hindrance at the selected reaction site. The TSEI descriptor is only related to the connectivity and atomic radius of substitutions and could be computed immediately, while Sterimol descriptors are calculated using Paton et al.'s code based on the 3D structures generated by RDKit (version 2020.09.3). The specific atoms & bonds chosen vary on reaction type and mechanisms to fully include the reaction information and chemical insights (Figure ).