Eddy is a Computational Fluid Dynamics (CFD) simulation software for natural ventilation and outdoor comfort analysis in buildings. Natural ventilation can significantly reduce cooling loads in buildings, however, modeling a building’s natural ventilation performance remains challeng- ing. Simulations are difficult to set up and due to the many physical and computational variables involved. As a result, the simulations are expensive, and they are usually employed not until the very end of the design process — often resulting in design alterations no longer being feasible. Eddy provides a user interface streamlined for architects and urban designers that is easy to use yet powerful and rich of features to make it easy to conduct natural ventilation simulations from the earliest design stages onwards. Further, Eddy provides optimized of meshing methodologies for urban wind flow models and the generation of wind pressure coefficients for airflow network simulations.