UX designers define digital products that shape our modern world. They are at the very beginning of product development and can directly influence the impact the products generate. However, little attention is paid to sustainability values in day-to-day business, which has a counterproductive effect on all dimensions of sustainable development. This thesis explores how a digital co-design toolkit can help UX design (UXD) practitioners find ways to integrate sustainable values into their daily work. Thematically, this project focuses on the UN Sustainable Development Goals (SDGs). On the one hand, to ensure a holistic point of view on the topic of sustainable development. On the other hand, to provide an approach to contribute to the SDGs from the UXD field. This research builds upon Sustainable Interaction Design (SID) theories, and a participatory design approach is pursued using a co-design process. The result of this work is a digital toolkit, which is designed for a collaborative online whiteboard platform for UX practitioners. The thesis contributes knowledge to the field of Interaction Design by proposing a toolkit for sustainable UX design.