As the world is becoming increasingly urbanized there is a need for more sustainability-oriented planning of our cities. Policy and decision-makers are interested in the use of evidenced based approaches and tools that will support collaborative planning. There are a number of tools in the domain of spatial planning and decision support systems that have been built over the last few decades but the uptake and use of these tools is somewhat limited. <br><br> In the context of Australia there is significant urban growth occurring across the major cities and a need to provision planners and developers with precinct planning tools to assist in managing infill and the densification of the existing urban fabric in a carbon constrained economy. In this paper we describe the development of a new precinct planning tool known as the Envision Scenario Planner (ESP), which is being applied initially in two cities, Melbourne and Perth to assist in the urban design and planning of Greyfield sites. <br><br> To set the scene in this paper we firstly provide a brief review of the existing state of play of visualization and modelling tools available to urban planners in Australia. The focus on the paper will be to introduce an iterative co-design prototyping approach for developing a best practice precinct planning support tool (ESP) from an earlier tool known as ENVISION. The first step of the approach is an exposure workshop with experts to refine the proposed tool workflow and its functionality. Subsequent iterations of the prototype are then exposed to larger audiences for validation and testing. In this paper we will describe the process and the preliminary findings in implementing the first phase of this iterative co-design prototype approach.