The paper aims at providing a procedural and instrumental framework for enabling massive citizen participation in urban planning projects via digital collaboration and communication tools. Derived from a structured analysis of existing formal and informal participation processes in urban development we developed a comprehensive process supported by specific digital tools for massive participation. This so-called Minimal Viable Process fulfils a) good practice standards for participation while b) utilising as few as possible technical means and procedural steps. For this purpose, several workshops with authorities and professional designers have been performed to estimate the advantages of the different strategies. In a next step, the necessary tools and their interlinkages were developed and tested with a test-run of the process and with mockup-tools (Dummy Testbed). Going beyond existing participation processes in urban development, the newly developed procedure ensures proper citizen involvement from the very start of a project up to design selection, plus a lean and feasible conduct of the overall campaign. The framework involves all necessary stakeholder groups, who are addressed by specific tools and algorithms. The test-run of the process and its tools (“Dummy Test Bed”) was performed in Spring 2018 under laboratory conditions, utilising a real world project case but within a controlled experimental environment. The results indicate the general applicability of the process and the tools, and provided insight for the further technical development of the IT tools and the procedure itself within the H2020 project “U_CODE Urban Collective Design Environment”.