The AT Protocol (ATProto) is a decentralized data layer for the web that enables user-owned data storage and control, addressing issues like data loss, walled gardens, and lack of interoperability in centralized platforms. Users store their data in personal folders - essentially repositories for JSON records - hosted either by themselves or third-party providers, with apps acting as consumers and creators of this data rather than its owners. This architecture allows users to switch apps or hosting providers without losing content, ensuring continuity and portability across services.
The protocol supports a wide range of applications beyond social media, including blogging, forums, code hosting, and music tracking (e.g., Teal FM), all built on a shared, open infrastructure. It uses flexible schema definitions called lexicons, which allow developers to define custom data types while enabling interoperability when desired. Data is publicly accessible by default, with event streaming via WebSockets allowing apps to sync and display content. The system draws comparisons to RSS and Git, emphasizing decentralized ownership, algorithmic flexibility, and community-driven standardization, while avoiding the rigidity of fully centralized platforms or blockchain-based systems.