Strategic energy planning decisions are crucial for addressing climate change and energy security concerns. A new modelling framework has been developed to help decision-makers understand the energy system better. This framework shows how policy and investment choices impact energy consumption, costs, and the environment. The model breaks down energy consumption into heating, electricity, and transportation, and considers the competition between electricity and fuels in different sectors. By using a monthly resolution, seasonal energy system issues are highlighted. The framework is designed to be easily adaptable to different large-scale energy systems and is currently being used in an online energy calculator for Switzerland.