Mordred is a new molecular descriptor calculation software that can calculate over 1800 two- and three-dimensional molecular descriptors. It is freely available via GitHub and can be used in the command line interface, as a web application, or as a high-flexibility Python package on all major platforms. Mordred is at least twice as fast as PaDEL-Descriptor and can calculate descriptors for large molecules that other software cannot. It is open-source and released under a 3-clause BSD license, allowing both commercial and non-commercial use. Mordred is easy to install and use, supports a wide range of molecular descriptors, and includes automated tests. It can calculate descriptors for large molecules efficiently, and its performance is validated through benchmark tests. Mordred is designed to be flexible, with the ability to calculate uncommon-range descriptors without modifying the source code. It also supports automated tests and has a web interface for non-Python users. Mordred is compared to other software programs and is found to be superior in several aspects, including ease of use, flexibility, and speed. It can be used for cheminformatics studies, such as those on quantitative structure–property relationships. Mordred is available as a web application and can be installed on a server for use by multiple users. It is also available as a CLI and can be used for large-scale calculations. Mordred is a promising choice for molecular descriptor calculation software due to its performance, convenience, number of descriptors, and lax licensing constraint.Mordred is a new molecular descriptor calculation software that can calculate over 1800 two- and three-dimensional molecular descriptors. It is freely available via GitHub and can be used in the command line interface, as a web application, or as a high-flexibility Python package on all major platforms. Mordred is at least twice as fast as PaDEL-Descriptor and can calculate descriptors for large molecules that other software cannot. It is open-source and released under a 3-clause BSD license, allowing both commercial and non-commercial use. Mordred is easy to install and use, supports a wide range of molecular descriptors, and includes automated tests. It can calculate descriptors for large molecules efficiently, and its performance is validated through benchmark tests. Mordred is designed to be flexible, with the ability to calculate uncommon-range descriptors without modifying the source code. It also supports automated tests and has a web interface for non-Python users. Mordred is compared to other software programs and is found to be superior in several aspects, including ease of use, flexibility, and speed. It can be used for cheminformatics studies, such as those on quantitative structure–property relationships. Mordred is available as a web application and can be installed on a server for use by multiple users. It is also available as a CLI and can be used for large-scale calculations. Mordred is a promising choice for molecular descriptor calculation software due to its performance, convenience, number of descriptors, and lax licensing constraint.