Cities have begun to apply circular economy principles to the built environment to reduce waste and CO2 emissions in the construction sector. Recent research and practice have focused on developing tools to support municipal decision-making processes in assessing the circularity of construction projects. However, there is a lack of understanding of how such tools are used and how they shape circularity in decision-making processes. Using an evidence-based policymaking lens, this article studies how using a circular assessment tool supported municipal decision-making to realise a circular housing project in Nijmegen, the Netherlands. Results are based on interviews and an analysis of policy documents and all information that was created for and during the tender procedure. The analysis shows that how the circular assessment tool was used, depended on stakeholders’ interests and the stage of the decision process. On the one hand, the tool stimulated circular solutions by helping to compare quantifiable results, but, on the other hand, the predefinition of the circular criteria narrowed down the final design and created a focus on the adaptability of the building in the future instead of a focus on the reuse of existing materials. The article shows that the use of evidence to realise circular ambitions, requires new skills of municipalities and demands both continuous support from experts as well as more strict criteria and ways to measure circularity in governmental regulations to stimulate the use of circular materials in the built environment.