Online disinformation and fake media content have emerged as a serious threat to democracy, economy and society. Content verification is currently far from trivial, even for experienced journalists, human rights activists or media literacy scholars. Moreover, recent advances in artificial intelligence (deep learning) have enabled the creation of intelligent bots and highly realistic synthetic multimedia content. Consequently, it is extremely challenging for citizens and journalists to assess the credibility of online content, and to navigate the highly complex online information landscapes. WeVerify aims to address the complex content verification challenges through a participatory verification approach, open source algorithms, low-overhead human-in-the-loop machine learning and intuitive visualizations. Social media and web content will be analysed and contextualised within the broader online ecosystem, in order to expose fabricated content, through cross-modal content verification, social network analysis, micro-targeted debunking and a blockchain-based public database of known fakes. A key outcome will be the WeVerify platform for collaborative, decentralised content verification, tracking, and debunking. The platform will be open source to engage communities and citizen journalists alongside newsroom and freelance journalists. To enable low-overhead integration with in-house content management systems and support more advanced newsroom needs, a premium version of the platform will also be offered. It will be furthermore supplemented by a digital companion to assist with verification tasks. Results will be validated by professional journalists and debunking specialists from project partners (DW, AFP, DisinfoLab), external participants (e.g. members of the First Draft News network), the community of more than 2,700 users of the InVID verification plugin, and by media literacy, human rights and emergency response organisations.