Open Babel is an open-source chemical toolbox that supports the interconversion of over 110 chemical file formats. It provides a wide range of cheminformatics algorithms, including partial charge assignment, aromaticity detection, bond order perception, and canonicalization. The software is freely available under an open-source license and is used by over 40 software projects. Open Babel allows users to search, convert, analyze, and store molecular data from various fields, including chemistry, biochemistry, and materials science. It includes utilities for conformer searching, 2D depiction, filtering, batch conversion, and substructure/similarity searching. The software is implemented in C++ and supports multiple programming languages through bindings. Open Babel has a modular design, with separate modules for chemical core, formats, conversion control, user interface, and fingerprinting. It also includes extensible interfaces for plugins, enabling the addition of new file formats and functionalities. The software includes a robust validation and testing framework, ensuring high-quality and reliable performance. Open Babel is used in various applications, including chemical database management, molecular modeling, and drug design. It is widely cited and has been adopted by many scientific communities. The project is open-source, with a cross-platform development model, and is continuously improved to support new molecular data formats and functionalities. Open Babel is available at http://openbabel.org and is freely accessible to users, developers, and researchers.Open Babel is an open-source chemical toolbox that supports the interconversion of over 110 chemical file formats. It provides a wide range of cheminformatics algorithms, including partial charge assignment, aromaticity detection, bond order perception, and canonicalization. The software is freely available under an open-source license and is used by over 40 software projects. Open Babel allows users to search, convert, analyze, and store molecular data from various fields, including chemistry, biochemistry, and materials science. It includes utilities for conformer searching, 2D depiction, filtering, batch conversion, and substructure/similarity searching. The software is implemented in C++ and supports multiple programming languages through bindings. Open Babel has a modular design, with separate modules for chemical core, formats, conversion control, user interface, and fingerprinting. It also includes extensible interfaces for plugins, enabling the addition of new file formats and functionalities. The software includes a robust validation and testing framework, ensuring high-quality and reliable performance. Open Babel is used in various applications, including chemical database management, molecular modeling, and drug design. It is widely cited and has been adopted by many scientific communities. The project is open-source, with a cross-platform development model, and is continuously improved to support new molecular data formats and functionalities. Open Babel is available at http://openbabel.org and is freely accessible to users, developers, and researchers.