As sustainability increasingly gains attention, it has also found its way into the area of software engineering, with a specific emphasis on reqirements engineering. The Sustainability Awareness Framework (SusAF) proposed by Duboc et al. supports stakeholders in taking the long view at their software systems in terms of sustainability. In this paper, we propose SusApp, a web-based tool to simplify the application of the SusAF, in particular the documentation and visualization of effects on sustainability. To learn about the users’ perception of SusApp, we conducted two small-scale user studies that investigated the tool’s usability and usefulness. Overall, the studies showed that the tool was generally perceived positively by the participants. However, shortcomings in the usability became apparent, which have also impacted the perceived usefulness.