ActivityPub

Federated Protocol

W3C Recommendation for decentralized social networking based on ActivityStreams 2.0, providing standardized client-to-server (C2S) and server-to-server (S2S) APIs for creating, updating, and deleting content as well as federating social activities across independently operated servers

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Details

License W3C Standard (implementations vary: Mastodon AGPL-3.0, Pleroma AGPL-3.0, Pixelfed AGPL-3.0, Lemmy AGPL-3.0, PeerTube AGPL-3.0, others MIT/Apache)
Dev Status 🏁 Final
Dev Status Detail Released (W3C Recommendation, January 23, 2018; widely implemented; Fediverse ecosystem with 10M+ accounts across thousands of instances)
Owner W3C Social Web Working Group (original authors: Christopher Lemmer Webber, Jessica Tallon, Erin Shepherd, Amy Guy, Evan Prodromou); now maintained by W3C Social Web Community Group
Owner - List
  • World Wide Web Consortium
Governing Body W3C (Recommendation track — Social Web Working Group) | W3C Community Group (Social Web CG, ongoing maintenance)
Governing Body - List
  • World Wide Web Consortium
Country International (W3C standard)
Start Year 2016
Stack Implementation-dependent (Mastodon: Ruby on Rails + Node.js; Pleroma/Akkoma: Elixir; Pixelfed: PHP/Laravel; Lemmy: Rust; PeerTube: TypeScript/Node.js)
Funding W3C (standards development funded by W3C member organizations); implementations funded separately (Mastodon: donations + EU grants; Pixelfed, Lemmy, PeerTube: donations/grants)
Funding - List
  • World Wide Web Consortium
Last Investigated Jan 15, 2026

Topology view

This tool in the centre and the things it is directly related to. Each line names the kind of relationship.

Topology view: ActivityPubThis tool in the centre and the things it is directly related to. Each line names the kind of relationship.ActivityPubElohim Protocol (Others aiming to interoperate with it)ElohimProtocolLinkedClaims (Others aiming to interoperate with it, Based on)LinkedClaimsNextGraph (Others aiming to interoperate with it)NextGraphATproto (Basis for)ATprotoCivic Activity (Basis for)CivicActivityFedID (Basis for, Conforming implementations, Interoperates with, Protocol spoken by)FedIDJSON-LD (Based on, Conforms to, Speaks protocol)JSON-LDRDF (Based on)RDFShelter Protocol (Basis for)ShelterProtocolValueflows (Basis for, Based on)ValueflowsActivityPods (Hosts)ActivityPodsBonfire Networks (Hosts, Protocol spoken by)BonfireNetworks

9 more related entities are not drawn; see the list below or open the Graph Explorer.

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Use Case Domains

Communication Group Formation & Governance Events & Coordination

Affordances

Protocol federation Cross-instance federation Consent-based audiences

Federated Protocol Attributes

Owner - List
  • World Wide Web Consortium
Origins Social networking / Federation (evolved from OStatus, Pump API, and earlier W3C Social Web Working Group work; ActivityStreams 2.0 as data model foundation)
Database Implementation-dependent (typically PostgreSQL; Mastodon uses PostgreSQL + Redis + Elasticsearch)
Query Language N/A (servers expose HTTP APIs per ActivityPub spec; no standardized query language; Linked Data Notifications for inbox delivery)
Data Formats JSON-LD (ActivityStreams 2.0 vocabulary; Activity, Actor, and Object types; compacted JSON-LD with @context)
Collaborative Live Editing N/A (designed for asynchronous social federation; not a collaborative editing protocol)
Rich Text Editing Application-level (clients typically support HTML/Markdown in content fields)
Mobile Support Yes (Mastodon iOS/Android, Tusky, Fedilab, Ice Cubes, Ivory, Pixelfed, etc.)
Web Support Yes (Mastodon Web, Pixelfed, Lemmy, PeerTube, BookWyrm, etc.)
Native Apps Yes (desktop and mobile clients across implementations)
Terms Self-hosting + Free public instances + Paid hosting services (e.g., masto.host, federation.spacebear.ee)
Funding - List
  • World Wide Web Consortium
Funds N/A (standard development funded by W3C; Mastodon gGmbH separately funded)
Based On ActivityStreams 2.0 (W3C Recommendation, data model); evolved from OStatus (Salmon, PubSubHubbub, Atom) and Pump API (pump.io by Evan Prodromou)
Governing Body - List
  • World Wide Web Consortium
Content Addressing No (location-based via HTTP URIs; not content-addressed)
E2EE N/A (not part of the ActivityPub standard; some implementations exploring E2EE for direct messages)
Signature HTTP Signatures (server-to-server authentication; signing HTTP requests with RSA or Ed25519 keys for federation; Linked Data Signatures also used by some implementations)
Permissions Server-based ACLs (to, cc, bcc addressing for audience targeting; public, unlisted, followers-only, direct visibility levels in Mastodon)
Semantic Web Compatibility JSON-LD / ActivityStreams 2.0 (built on semantic web standards; uses @context for linked data; Activity, Actor, Object types defined in AS2 vocabulary)
Federation Model Server-to-Server (S2S) via HTTP POST to Actor inboxes; servers deliver Activity objects to followers' inboxes and shared inboxes; Client-to-Server (C2S) API also specified but less commonly implemented
Instance / Server Requirements Moderate (can run on VPS; Mastodon: ~2GB RAM, ~20GB storage minimum; scales with user count and federation breadth)
Account Portability Partial (follower migration supported via Move activity; content/posts stay on origin server; Mastodon supports account redirect and follower transfer)
Discovery / Relay Architecture Instance-based discovery (WebFinger for user lookup; Actor URIs for profile resolution) + optional relays for content distribution across instances
Server Authority Model Full server authority (instance admins control users, content moderation, federation policy; can defederate from other instances; to/cc/bcc addressing for audience targeting)
Protocol Maturity / Standardization W3C Recommendation (January 23, 2018; formal W3C standard; ActivityStreams 2.0 also a W3C Recommendation)
Data Sovereignty Server-controlled (users' data stored on home instance; server admin has full access; user depends on instance operator)

Relationships

How this tool connects to other tools and organizations, from relationships reviewed by the OpenHaven data steward. They describe how projects connect, not how good they are.

Based on
Conforms to
Developed by
  • World Wide Web Consortium
Funded by
  • World Wide Web Consortium
Hosted at
  • World Wide Web Consortium
Speaks protocol
Standardized at
  • World Wide Web Consortium
Stewarded by
  • World Wide Web Consortium
Stores in
Interoperates with
Basis for
Conforming implementations
Hosts
Inspired
Others aiming to interoperate with it
Protocol spoken by