We present a case study on eco-feedback tools in the context of Vienna’s Aspern Seestadt. Utilizing an action-research based methodology, we engage the local community in cooperation with the aspern.mobil LAB to co-design a digital interactive tool visualizing the participants’ personal CO2-footprint. Following suggestions from related literature and spanning the bow towards critical algorithm studies, we put a special focus on the explainability of the tool and the algorithmic calculations involved in determining the footprint, and evaluate that approach in terms of its transformative potential. Our findings show the educational value and increased awareness resulting from the use of our prototype and shed light on some issues of interface design and trust related to explainable algorithmic processes. Furthermore, in evaluating our research methodology we find action-research based methodologies highly suitable for local communities in relation to sustainable eMobility practices.