Urban climate models can help cities design efficient climate adaptation and mitigation strategies. Yet, most codes are not user friendly and they are written in proprietary programming languages. A case in point is UT&C – a widely used model for urban climate and hydrology with a detailed vegetation scheme particularly suited for the description and design of urban greening strategies. However, the original code was written in a Matlab and it was computationally heavy, thus hindering its wider use and applications. By translating the UT&C code into Julia, the FAIR-CITIES project has created an open, FAIR, and user-friendly software. More than 24’000 lines of code have been translated, fundamentally re-architecturing the model to be more modular and efficient. The new Julia code, UrbanTethysChloris.jl, has been extensively validated and benchmarked against the original MATLAB version. The model is now more accessible to less-advanced users and runs 3 to 5 times faster, thus opening new scientific opportunities (e.g., city-scale simulations, model coupling). The model is hosted on GitHub, in a repository that will be made publicly open to the community for contributions with extensive documentation and tutorials. Going forward, UrbanTethysChloris.jl is expected to facilitate a community-based development (with rigorous testing and benchmarking), increasing its accessibility and uptake by the broader urban climate and urban planning communities.