Achieving Europe’s mid-term decarbonization targets by 2030 is an ambitious challenge for local authorities. However, small and rural municipalities face significant barriers, including structural, institutional and economic challenges. To facilitate the achievement of this ambitious goal, it is essential to strengthen local administrative capacities through targeted support. This is indeed the main objective of the European LIFE22-CET LOCAL GoGREEN project, which is aimed to accelerate the clean energy transition in six small communities across Bulgaria, Croatia, Slovenia, Italy, Germany, and Spain. In particular, it supports them in developing strategic actions in five priority areas: sustainable transport and e-mobility, energy efficiency in buildings, renewable energy expansion, land-use planning for carbon sequestration, and waste-to-energy solutions. This is achieved through a range of activities, including stakeholder engagement, local capacity building, providing analytical tools for energy planning, conducting pre-feasibility studies, and developing roadmaps and action plans. This paper presents the groundwork for the preparation of action plans and feasibility studies by the pilot cities, i.e. the characterization of the state of the art from an energy and planning perspective. It focuses on the analysis of the self-assessments carried out by the pilot cities, the database of their current climate and energy plans and programmes, and the definition of a common set of key indicators to characterize their planning performance. The results obtained so far show a two-speed behavior in the planning practices of small municipalities across Europe, with lagging municipalities able to learn and adopt good practices from the leading examples in the project in horizontal mainstreaming.