Open Babel is an open-source chemical toolbox designed to handle the interconversion of chemical structures between various formats. It supports over 110 file formats, including common cheminformatics formats like SMILES, InChI, and MOL, as well as formats from computational chemistry packages, crystallography, and molecular dynamics software. The tool provides a wide range of cheminformatics algorithms, such as partial charge assignment, aromaticity detection, bond order perception, and canonicalization. Open Babel also offers utilities for conformer searching, 2D depiction, filtering, batch conversion, and substructure and similarity searching. It can be used as a programming library for developers in areas like organic chemistry, drug design, materials science, and computational chemistry. The software is freely available under an open-source license and has been widely adopted, with over 400 citations and contributions from a global community.Open Babel is an open-source chemical toolbox designed to handle the interconversion of chemical structures between various formats. It supports over 110 file formats, including common cheminformatics formats like SMILES, InChI, and MOL, as well as formats from computational chemistry packages, crystallography, and molecular dynamics software. The tool provides a wide range of cheminformatics algorithms, such as partial charge assignment, aromaticity detection, bond order perception, and canonicalization. Open Babel also offers utilities for conformer searching, 2D depiction, filtering, batch conversion, and substructure and similarity searching. It can be used as a programming library for developers in areas like organic chemistry, drug design, materials science, and computational chemistry. The software is freely available under an open-source license and has been widely adopted, with over 400 citations and contributions from a global community.