A PDS, or Personal Data Server, is the AT Protocol service that hosts a user's repository and handles authenticated account operations. It is the part of the network most directly responsible for storing the signed stream of records associated with an AT Protocol account.
What the PDS stores
An account's repository is a cryptographically verifiable collection of records such as posts, follows, profile data and other Lexicon-defined objects. The PDS accepts authenticated writes, maintains the repository, serves blobs such as media and exposes protocol endpoints used by clients and other infrastructure. Changes are emitted into the wider AT Protocol data stream so relays can ingest them. Identity is separated from any one PDS through decentralised identifiers, allowing the protocol to support migration between hosting providers rather than permanently binding an account to one server hostname.
Why AT Protocol separates hosting from aggregation
The architecture differs from both a central social platform and a typical ActivityPub instance. A PDS is primarily a user's data host, while aggregation, feeds, search and many application views can live elsewhere. That separation means a third party can potentially host accounts without recreating every part of the Bluesky application stack, and users can in principle move their repository while preserving a stable DID-based identity.
A PDS is only one part of the stack
A PDS is not necessarily a private box that only its user can inspect; much AT Protocol social data is intentionally public and replicated. Running a PDS also does not by itself make someone independent of relays or AppViews if they still rely on those services for discovery and presentation. The practical portability story depends on compatible infrastructure and clients, not just the protocol's abstract separation of roles.
Related reading
- What Is an AT Protocol Lexicon? How Bluesky Defines New Types of Data
- What Is NodeInfo? The Metadata Standard Used by Fediverse Servers