ActivityPub

ActivityPub is a protocol and open standard for decentralized social networking. It provides a client-to-server (C2S) API for creating and modifying content, as well as a federated server-to-server (S2S) protocol for delivering notifications and content to other servers. ActivityPub is the defining standard of the Fediverse, a decentralised social network of various social interaction models, and content types, which consists of independently managed instances of software such as Mastodon, Pixelfed and PeerTube, among others.

ActivityPub, AT Protocol, and more!

Talking about this article and how ActivityPub and AT Protocol are maybe not as different as people might think. We covered some slides to an unrecorded talk of mine, which explores a lot of things...

ActivityPub

The ActivityPub protocol is a decentralized social networking protocol based upon the [ActivityStreams] 2.0 data format. It provides a client to server API for creating, updating and deleting content, as well as a federated server to server API for delivering notifications and content.

ActivityPub

The ActivityPub protocol is a decentralized social networking protocol based upon the [ActivityStreams] 2.0 data format. It provides a client to server API for creating, updating and deleting content, as well as a federated server to server API for delivering notifications and content.

Why ActivityPub is the future

We often tout things like “Mastodon is based on open web protocols” as one of its advantages. I want to elaborate why exactly that’s a good thing.

ActivityPub Client API: A Way Forward | Steve Bate

The ActivityPub Client-to-Server (C2S) protocol was envisioned as a cornerstone of the decentralized social web, along with the Server-to-Server (S2S) protocol. Standardized by the W3C in 2018, C2S defines how user-facing applications, such as mobile apps or web clients, and bots should interact with social servers using Activity Streams 2.0 and JSON-LD. In theory, it ... Read more

Decentralization Trade Offs in AT Protocol and ActivityPub DWeb Camp 2026

Christine Lemmer Webber is lead author and co-editor of the W3C ActivityPub specification. Daniel Holmgren is Head of Protocol at Bluesky, working on the AT Protocol specification at the IETF. Join us for a discussion on decentralization trade-offs and other design decisions in the two protocols, and what that means for different architectures, structures, and even future points of convergence. Moderated by Boris Mann

A conceptual model of ATProto and ActivityPub

If you were to design an open social networking protocol, what would that look like? Which metaphors and comparisons would you use to get a general idea of how the network functions? And what would you answer if people ask if your network is decentralised and federated?

Social Networking Utopia — Matt

In discussing the network topology of social networks — whether centralized like Facebook or federated like ActivityPub — I think the ult...

Recently I’ve been thinking about a couple of... - Adam Wood

Recently I’ve been thinking about a couple of different tech-related things that sort of overlap. One is the (emerging) shape of the new social web; the other is a pull I’m feeling to try and lessen reliance on American companies.  I’ve been interested in / concerned by what became of social media for some time.1 Since the sundering of Twitter in 2022, I’ve kept an eye on the various alternatives, with particular interest in Mastodon and Bluesky. Actually, to be more accurate, my interest has been in the protocols behind those platforms: ActivityPub and AT Protocol respectively. Both have their...

Seeing the Politics of Decentralized Social Media Protocols

Calls to decentralize feed-based social media have been driven by concerns about the concentrated power of centralized platforms and their societal impact. In response, numerous decentralized social media protocols have emerged, each interpreting “decentralization” in a different way. We analyze four such protocols (ActivityPub, AT Protocol, Nostr, and Farcaster) drawing on protocol documentation, media coverage, direct usage, and semi-structured interviews with protocol developers and experts to situate each protocol within its socio-technical goals. To support this analysis, we develop a grounded lexicon that facilitates the description and comparison of analogous components across each protocol. With it, we show how each protocol distributes control over key components differently, shaping who holds power over critical aspects such as user identity, curation, and infrastructural ownership. By examining protocols as socio-technical artifacts, we show how they prioritize different values and make distinct trade-offs, providing CSCW researchers with a lens to more effectively evaluate and design future decentralized social media systems.

AT Protocol - AT Protocol

The AT Protocol is an open, decentralized, and high-performance network for building social applications.