In this paper, a probabilistic simulator for the upcoming FIFA World Cup is developed. For that, we develop a simulation model that can predict the outcome of a match by calculating a win expectancy for both participating teams based on several rules, that take into account different rating methods and can be arbitrarily weighted and combined by the user. The process of deriving the rules' formulae, if not available, from historical FIFA World Cup matches is described as well as the methods for calculating the probability for a draw and the expected number of goals in a match. Further, the resulting application, which does not only include the program to run the simulation, but also a web front end and a back end, which allow straight-forward user interaction with the simulator, is described.