A new online tool to assess solar and daylight access over the surfaces enclosing an urban canyon (i.e. building façades and street) is presented. From a limited series of parameters, users can easily describe the orientation and geometry of an urban canyon and precisely define an area of interest for which the calculations have to be performed. By implementing an original calculation method based on stereographic pictures, this tool aims both to demonstrate its capabilities and to serve for architectural and urban planning educational purposes. Its main advantage is that, beside providing numerical indicators (e.g. solar exposure, solar irradiation, sky view factor, daylight sky component) that can take inter-reflections into account, it also allows to visually interpret the results in a rather intuitive manner. The calculation method is available as an open source software package. It can serve to assess solar and daylight access in more complex urban forms.