The pressure to deal with urbanisation and environmental challenges strain current urban planning institutions. Translating sustainable development into urban planning practice is an urgent task for urban planners, to secure future needs of cities. A gap in literature is identified, and this research questions how urban planners operationalise sustainable urban development through sustainability tools in urban planning practice. This research explore practice cases and urban planners’ stories from Copenhagen-, Odense-, and Aalborg Municipality, in relation to how they have designed sustainability tools and practices of sustainable urban development planning; how they are reflexive; and how they positions themselves in the tension between practice and theory of sustainable development. To achieve the goals of sustainability it is crucial to develop an urban planning practice, by which urban planners can communicate and facilitate sustainable development. There are, however, challenges for the urban planners in finding their legal authority role as well as their role as process- and dialogue facilitators, by which the tools are representations of the need for more collaboration and coordination between actors, in order to cope with current institutions ill-equipped to cope with the ideals of sustainable development.