We present DELIBERATION.IO, an open-source digital platform designed to facilitate structured deliberation and democratic engagement at scale. The platform addresses critical gaps in existing civic technology through a modular architecture that supports a range of deliberation scenarios.

DELIBERATION.IO is designed with the following principles: (1) Open science: the platform incorporates evidencebased design informed by deliberative democracy research and supports future research in this direction; (2) Transparency: the platform is fully open-source and is accessible to everyone; (3) Flexibility: a modular architecture accommodates diverse deliberative formats from citizen panels to organizational decision-making; (4) Human agency: AI augments rather than replaces human judgment, ensuring participants retain control over their deliberative experience; and (5) Accessibility: universal design principles and cross device support ensure inclusive participation across diverse populations. DELIBERATION.IO enables researchers and practitioners to easily design and monitor complex deliberative processes in diverse settings. All components are released under the MIT license to support collective efforts in building evidence-based civic engagement tools.

The platform is publicly available at https://deliberation.io.