The Circularity Assessment Protocol (CAP) is a standardized assessment diagnostic tool to inform decision-makers through collecting community-level data on plastic usage and management. Grounded in materials flow and systems thinking concepts, the CAP uses a hub-and-spoke model to holistically characterize how consumer plastic flows into a community, is consumed, and flows out, either through waste management systems or leakage into the environment. The model consists of seven spokes: input, community, material and product design, use, collection, end of cycle, and leakage.