Pacti is an open-source Python package for carrying out compositional system analysis and design. Pacti represents components in a system using assume-guarantee specifications, or contracts. Pacti's capabilities, among others, include the following: Obtaining sensible system specifications from the specifications of the constituent subsystems. Computing specifications of subsystems that need to be added to a design in order to meet an objective. Diagnosing incompatibilities when interconnecting components. Documentation can be found on the project's website: www.pacti.org. For questions about Pacti and to interact with the community, please go to the organization's GitHub Discussions page. Pacti's developers can be reached at [email protected]. The Pacti project can be acknowledged by citing Inigo Incer, Apurva Badithela, Josefine Graebener, Piergiuseppe Mallozzi, Ayush Pandey, Sheng-Jung Yu, Albert Benveniste, Benoit Caillaud, Richard M. Murray, Alberto Sangiovanni-Vincentelli, and Sanjit A. Seshia. "Pacti: Scaling Assume-Guarantee Reasoning for System Analysis and Design." ArXiv abs/2303.17751 (2023).