When modelling outdoor microclimates, researchers and designers need to be aware of the modelling capabilities and limitations of tools. This comparative study attempts to understand how tools such as CitySim Pro, ENVI-met, RayMan, Grasshopper plug-ins Honeybee / Ladybug and Autodesk CFD, evaluate the Mean Radiant Temperature (MRT), one of the main parameters governing human energy balance. To this purpose, the space underneath and surrounding the Rolex Learning Center, located on the EPFL campus in Lausanne, were modelled. Significant variations of MRT predictions were recorded. This led to the review of the physical modelling assumptions that each of the calculation engines operates. Based on the tools’ available documentation, answers to forums, interviews with the developers, and tool codes, the paper lists how all the variables that affect MRT are considered. Although not exhaustively, the paper lists the main differences among tools, leading to the understanding of the types of physical context that they could simulate.