In this session, I will tell the story of the Your COVID-19 Risk tool and how it was developed. The Your COVID-19 Risk project is a volunteer project: no funding, but over a hundred volunteer experts working together to create a tool to help people decrease their COVID-19 related risk. The tool is underpinned by a risk model and presents tool users with a series of questions about determinants to enable us to improve the tool, as well as a behavior change intervention aiming to promote distance keeping, hand washing, and staying at home. This project would not have been possible without a backbone that solidly structured the project to leverage theory and evidence. This backbone is provided by a number of cutting edge technologies, and in this session, I will highlight two of them: Acyclic Behavior Change Diagrams (ABCDs) and Decentralized Construct Taxonomies. The former enables a comprehensive and machine-readable description of the structural and causal assumptions underlying a behavior change intervention. This is a useful tool when developing an intervention, but also when improving one or reporting on it. ABCDs also eliminate much of the need for coding BCTs when doing systematic reviews or meta-analyses. Decentralized Construct Taxonomie specifications facilitate decentralized unequivocal construct definitions that are accompanied by corresponding instructions for, in this case, developing measurement instruments. These somewhat abstract technologies and their uses will be illustrated at the hand of the Your COVID-19 Risk project.