Municipalities and cities are important drivers of decarbonizing energy systems. They are responsible for setting a strategic direction to increase energy efficiency, produce renewable energy, and reduce local greenhouse gas emissions. They are essential in mobilizing stakeholders and citizens to introduce energy solutions for climate neutrality. However, this potential is not yet well exploited due to a lack of skills and supportive tools. It is very difficult for municipalities to calculate and understand today's CO2 emissions and even more to understand different possible future scenarios. The project aims to increase the capacity of municipality staff and local stakeholders to deal with energy transition issues. The major practical outcome is a new computer-based simulation model called CommitClimate Simulator for carbon footprint calculation and future scenario modeling. Local authorities will develop, test, and use the Simulator to create municipal sustainable energy and climate action plans for reaching climate neutrality. The technical work on the development and use of the modeling tool goes hand in hand with information & communication activities and training for target groups and citizens. All results and experiences are summarized in an interactive online platform with step-by-step explanations, the CommitClimate Simulator, and training materials enabling its use in energy transition planning for every municipality.