The International Federation for Housing and Planning (IFHP) is in the lead of a newly developed planning tool, called the Social Cities Programme (SCP), which is being tested in five Danish municipalities: Frederiksberg, Gladsaxe, Middelfart, Skive and Aalborg. The SCP aims at simplifying the complexity of social sustainability through a quantitative index – a methodology pertaining to a particular conception, which is sought diffused to the five Danish municipalities. To address this problem, the following research question has been posed: How is the IFHP’s Social Cities Programme (SCP) functioning as a governance tool to shape Danish municipal conception and practice of social sustainability? The research finds that the SCP is launched in the wake of an internal crisis in the IFHP, for which reason there is a bias in the visible agenda of enhancing the social sustainability of cities. Due to the SCP’s appealing format is has functioned as a governance tool in two municipalities, where ongoing projects were ready to implement the SCP’s methodology. It is moreover found, that two other municipalities already have a conception and practice of social sustainability aligned with the SCP, as it is politically prioritised. It is therefore argued, that the SCP potentially can function as a governance tool in other municipalities as well, depending on factors such as timing, political landscape, interdisciplinary collaboration and existing planning practice. Finally, it is argued that the complex nature of social sustainability, to a certain extent, can be handled through the use of indices, however with the risk of depoliticising social sustainability and potentially urban planning, for which reason indices must be informative rather than guiding.