Civil society and public authorities from all levels of government are increasingly turning to digital democracy tools to improve citizens’ participation in democratic processes and the legitimacy of policy decisions. At the same time, digital democracy technology today is not yet fit to meet the lofty goal of providing an all-round democratic infrastructure that can re-empower citizens and make public administrations more relevant and responsive to the citizenry’s wills and needs. This is because digital democratic technology is currently developed and deployed while we still lack evidence-based methods to design, assess and validate it. We still lack the know-how to discern which specific technological solutions best foster inclusive, meaningful and scalable democratic participation, and under what conditions. PERYCLES tackles the challenge of developing such know-how, analyzing and testing platform designs on an open-source software for democratic deliberation that can be deployed at multiple levels of governance: from local, to national, to transnational. To do so, we develop a first-of-its-kind interdisciplinary approach to the design of digital democracy technology, which integrates methods and concepts from democratic theory, the social sciences and the computing sciences. The outcome of the project will be threefold: first, a set of methods to assess digital democracy solutions in a principled manner; second, readily available open-source implementations of digital democracy solutions that meet the identified standards; third, a library of best practices and recommendations for the design and deployment of online participation platforms, targeting digital democracy practitioners, citizens and decision-makers.