In order to facilitate urban energy management and energy planning, the project MEU developed a web based tool as a decision support system for decision makers. Using a web based approach minimizes the effort on the client site as no software needs to be installed or be updated on the personal computer. Updates are published by the development team on the central server. During the first phase of the project, First, data are collected based on the buildings in the federal land registry offices' data. The data contains all the relevant elements in the energy conversion chain of a given city over the last couple of years available on an annual basis: meteorological data, a list of accessible resources, energy conversion technologies, energy distribution networks and buildings as consumers of different energy services. Second, all buildings and networks are geo-referenced to allow plotting maps. This already gives a comprehensive overview of the current energy state of a city. Third, measurements of (annual) energy consumptions are introduced allowing the performance monitoring. With the annual energy consumption of each energy conversion system, the current state of a city can be monitoring and compared to previous years. Fourth, this data is structured and completed for the use in the energy simulation software: CitySim for the dynamic building energy demand simulation and EnergyTechnology for the calculation of the energy conversion technologies. Especially the completion demands supplementary work as the data sets are often not very comprehensive. Therefore default values based on the current Swiss norms and previous publications are used to minimize the errors made in the simulations. As a set of default values is provided in the platform, it runs even if only a small data set is imported. When more information is available such as the energy consumption or the physical building data, the platform can easily be updated to increase the accuracy of the results. With this approach, urban energy flows from resource to useful energy can be tracked and inefficiencies can be spotted easily along the conversion processes. Furthermore, the creation of scenarios based on a given actual year allows for example the quick comparison of different energy conversion scenarios for different technological measures introduced in a city or the evaluation of refurbishment strategies on the energy demand. The maps allow to geo-localize priority areas and help representing the results.