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As Elon Musk’s Category 5 tweet storm continues, the once-obscure social network Mastodon has been gaining more than 1,000 new refugees per hour, bringing its user base to about eight million.
Participating as a user is quite easy. More than enough ex-Twitterers are happy to find a Mastodon instance via joinmastodon.org, get a list of handles for their Twitter friends via Movetodon, and carry on as before.
But what new converts may not realize is that Mastodon is just the most prominent node in a much wider movement to change the nature of the web.
With a core purpose of decentralization, Mastodon and its relatives are “federated”, meaning you may set up a server as a home base for friends and colleagues (an “instance”), and users of all instances can communicate with users on yours. The most common metaphor is email, where yahoo.com, uchicago.edu, and condenast.com all host a local collection of users, but anyone can send messages to anyone else using standard messaging protocols. With cosmic ambitions, the new federation of freely communicating bodies is called “the Fediversum”.
I started using Mastodon in mid-2017 when I vaguely heard the initial buzz. I found that the people who inhabited a world whose first major selling point was its decentralized network topology were nerdy and counter-cultural. There were no #brands. Servers were (and are) operated by academic institutions, journalists, hobbyists and activists in the LGBTQ+ community. The organizers of one agency, scholar.social, host an annual series of seminars, where I have presented.
The decentralization aspect that was such a selling point for me was also a core design goal for Mastodon and the predecessors it built on, such as GNU Social. In an interview with Time, lead developer Eugen Rochko said he started developing Mastodon in 2016 because Twitter was becoming too centralized and too important to discuss. “Maybe it shouldn’t be in the hands of a single company,” he said. His desire to build a new system “generally had to do with a sense of distrust of the top-down control that Twitter wielded.”
Like many web apps, Mastodon is an amalgamation of components and standards; hosting or interacting with a Mastodon instance requires some familiarity with all of these. Among them, and the headliner at the heart of The Fediverse, is the World Wide Web Consortium’s (W3C) ActivityPub standard, which specifies how actors on the network are defined and interact.
Mastodon and ActivityPub evolved at roughly the same time, with the first major release of Mastodon in early 2017 and ActivityPub being finalized as standard by W3C in January 2018. is useful in many contexts other than reporting what users had for lunch.
Like Mastodon, ActivityPub represents a rebellion against an increasingly centralized web. Christine Lemmer-Webber is the lead author of the 2018 ActivityPub standard, based on previous work led by Evan Prodromou on another service called pump.io. Lemmer-Webber tells Ars that when developing the ActivityPub standard, “We were the only standards group at the W3C that had no corporate involvement… None of the big players wanted to do it.”
She felt that ActivityPub was a success for the idea of decentralization even before reaching millions of users in recent months. “The assumptions you might have, that only the big players can play, turned out to be wrong. And I think that should be really inspiring for everyone,” she said. “It’s inspiring to me.”
Set standards
The idea of an open web where actors use common standards to communicate is as old as, well, the web. “The dreams of the 90s live in the Fediverse,” Lemmer-Webber told me.
In the late ’00s, there were plenty of isolated, incompatible networking and sharing systems like Boxee, Flickr, Brightkite, Last.fm, Flux, Ma.gnolia, Windows Live, Foursquare, Facebook, and many others that we loved, hated , forget, or wish we could forget. Several independent attempts to standardize inter-silo collaboration generally converged on the Activity Streams v1 standard.
Both the original Activity Streams standard and the current W3C Activity Streams 2.0 standard used by Mastodon and friends provide a grammar for expressing things a user might do, such as “make a post” or “like👍 a post with a certain ID” or “request to befriend a certain user.” The vocabulary one would use with this grammar is broken down into its own substandard, the Activity Vocabulary.
Now that we have a way to express a person’s stream of thoughts and actions in JSON blobs, where do all these streams go? The ActivityPub standard is an actor-based model that specifies that servers must have a profile for each actor with a universal resource indicator (URI) for each actor’s inbox and outbox. Actors can send a GET request to their own inbox to see what the actors they follow have posted, or they can GET another actor’s outbox to see what that specific actor has posted. A POST request to a friend’s inbox puts a message there; a POST request to the user’s own outbox posts messages for everyone (with the appropriate permissions). The standard specifies that these different in- and outboxes contain activities in sequential order, much like our familiar social media timelines.
(PS: If you want to see what an activity stream looks like and your browser renders JSON nicely, just grab any outbox and watch.)
Here we have the vision of the Fediverse: a series of ActivityPub nodes, spread around the world, all speaking a common language. Mastodon is one of many attempts to implement the ActivityPub standard inboxes and outboxes. There are dozens of others, ranging from other microblogging platforms (“It’s like Mastodon, but…”) to an ActivityPub server running a chess club.
In theory, they all communicate with each other; in practice not so much. The sources of incompatibility stem from a variety of issues, from imperfections in the standard to questions about how to form online communities to attempts to move beyond the standard post/comment/follow format of typical social networks.
