Energy system models can contribute to the transition to low-carbon energy systems by helping devise pathways and calculate costs of energy policies and targets. As such, they are intended to provide support for energy planning, especially at the national level. Since energy system models are often developed outside urban contexts, their municipal policy relevance cannot be taken for granted. It is still unclear to what extent and how energy system models are applied to create municipal energy strategies and who uses them. This exploratory study aims to shed light on these aspects by examining the use of modelling tools and their outputs by municipal planners. We conducted interviews with practitioners from Danish municipalities and evaluated them using qualitative content analysis. This paper finds that the interviewees' use of software tools depends on how they perceive the functionality and complicatedness of the tools. The planners we interviewed prefer spreadsheet-based CO2 calculation or evaluation tools to energy system models, which in turn are used by heat supply companies, consultancies or universities. The practitioners we interviewed collaborate with model developers and users to further utilize model outputs. The incorporation of results from models or spreadsheet tools takes place mostly in the beginning of energy planning projects. This study suggests that models and the modelling practice can be improved with: open data, assumptions and models, collaboration across planning levels and improving links between technical modelling and practical implementation.