Due to global warming and contemporary architecture, which uses a lot of glass and lightweight constructions, the problem of summerly overheating of rooms is ubiquitous. There is a simplied method according to the Standard B 8110-3, which is predominantly used for assessing the summerly heat protection in Austria. However, due to the simplied calculation approach, no good planning reliability can be assured and is thus far from the more realistic results and possibilities of thermal dynamic building simulation programs. On the other hand building simulation programs are usually too complex and time-consuming to support architects in the design process. Many planning decisions, which are made in early planning phases, have signicant inuence on the summerly behaviour of the building and can hardly be changed afterwards or just with increased eort. Considerations regarding climate-friendly building should thus already take place in the design phase.^ ^Again, it is problematic that architects lack tools for evaluating the summerly heat protection that can be used easily. Hence the goal is to develop a generally accessible, intuitive online tool with a self-explanatory, playful interface that is not based on a simpli ed calculation method, but generates realistic results. The architects will then be easily enabled to develop optimized designs regarding the summerly heat protection. In the background, physically correct results are generated by means of a thermodynamic building simulation, based on a periodically settled calculation method in the frequency domain. Thanks to this method, which is especially suitable for the question of midsummer room temperatures, results can be obtained in real time and dierent variants can be analysed quickly. Moreover, important aspects such as heat storage capacity are discussed, in order to eliminate often prevailing misunderstandings.^ In addition, various methods for assessing the summer suitability are compared, as well as programs are presented that implement these methods. Furthermore, validations of selected thermodynamically building simulation programs are presented using the European Standard 13791.