Citizens are increasingly shaping their city selfdetermined. To do so, they use digital platforms to start projects, gain awareness or raise funds. These and other participation mechanisms enable citizens to participate in manifold ways. With the help of the tree ring model introduced in our contribution, we present a tool that is intended to support practitioners in evaluating and developing their platforms. The model was designed based on the analysis of 22 existing platforms as well as a literature review and evaluated in qualitative interviews. The result is a tree ring model that shows a new understanding of participation apart from hierarchical structures. The citizens’ role classification and the possible mechanisms that can offer practitioners effective implications for the design of participation platforms.