atprotocol

ATProto was developed by Bluesky as an open social protocol.

The AT Protocol is a networking technology created to power the next generation of social applications. The initial reference application, bsky.app,provides a global-scale microblogging experience.

Creation of an IETF working group is in progress, as of late 2025 / early 2026.

Protocol Overview

The Authenticated Transfer Protocol, aka atproto, is a federated protocol for large-scale distributed social applications. This document will introduce you to the ideas behind the AT Protocol.

From the Protocol Overview

Specification

The Authenticated Transfer Protocol (AT Protocol or atproto) is a generic federated protocol for building open social media applications. Some recurring themes and features are:

• self-authenticating data and identity, allowing seamless account migrations and redistribution of content
• design for “big world” use cases, scaling to billions of accounts
• delegated authority over application-layer schemas and aggregation infrastructure
• re-use of existing data models from the dweb protocol family and network primitives from the web platform

From the Specification

PDS

Personal Data Server. Similar in concept to Personal Data Store, except this is the software server and can host multiple user accounts.

• Bluesky Typescript Implementation bluesky-social/pds
• Related PDS posts on the community forum

See also ATProto Community Resources