EUNOMIA is a fully decentralised, intermediary-free and open-source solution for addressing three key challenges: which social media user is the original source of a piece of information; how this information has spread and been modified in an information cascade; and how likely it is to be trustworthy. Although its innovations are applicable across any social network, its design philosophy makes it ideal for evaluation on similarly open, decentralised and federated new social media networks, thus contributing against accumulation of power in the large social media intermediaries located outside Europe. EUNOMIA actively encourages democratic citizen participation in content verification by allowing voting on content trustworthiness and influencing the reputation of content generators and sharers. It combines information cascade verification with information trustworthiness scoring, benefitting from blockchain technology to ensure transparency of the scoring process and that information has not been modified in a cascade. It also places emphasis on ensuring that trustworthiness information is communicated transparently and accessibly. A General Data Protection Regulation (GDPR) compliant and ethically responsible digital companion running as a local app on the user’s device encourages the involvement of each user, while also carrying out the background processing for scoring and verifying content, and crucially for visualizing to the user. EUNOMIA uses social-science based co-design methodologies acknowledging and integrating users’ experiences of social media, specifically in how they use and trust the information they interact with. EUNOMIA’s versatility will be evaluated with large communities in social journalism and traditional media, as well as the largest user community of the most popular decentralised social media networks.