AT Protocol
social networking protocol
The AT Protocol (Authenticated Transfer Protocol, pronounced "at protocol", commonly shortened to ATproto or "ATP") is a protocol and set of open standards for decentralized publishing and distribution of self-authenticating data within the social web. It serves as the technical foundation of the Bluesky social network, originally developed as a reference implementation for the protocol, as well as an ecosystem of interoperable social applications and services collectively referred to as the ATmosphere.
The AT Protocol aims to address perceived issues with earlier decentralized social networking protocols such as ActivityPub and Nostr; these include user experience, semantic interoperability, discoverability, network scalability, and portability of user data and social graphs. It employs a modular microservice architecture and a federated, server-agnostic user identity to enable seamless movement between network services, with the goal of providing an integrated online experience without dependence on any single privileged entity.
As of January 2026, the protocol's general architecture, user repository, and data synchronization specifications are in the process of standardization within the Internet Engineering Task Force (IETF). Further specifications—including data schemas, identity systems, OAuth implementation, and private/limited visibility data—are under development by Bluesky Social PBC. The company has said it may seek to standardize additional specifications through the IETF in the future, depending on the outcome of current efforts.
Design
The AT Protocol is designed to facilitate the creation of federated identities, so that users can retain, manage, and customize one online identity across multiple platforms and services. Independent hosts and other network participants can access and serve any user content within the network by fetching content formatted as predefined data schemas from federated network-wide data streams. Bluesky Social describes the protocol as being "modeled after the open web".
Compared to other protocols for social networking such as ActivityPub, where implementations are typically designed as a monolithic server that hosts both user data and the application, it splits up these elements into smaller microservices, which can be used as needed.
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This entry incorporates text from “AT Protocol” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.