Mastodon (social network)
Mastodon is a free and open-source, decentralized microblogging social network built around the concept of federation: independent servers (“instances”) interoperate to form a larger network often referred to as the fediverse. Mastodon’s server-to-server communication is based on the ActivityPub protocol, a W3C standard for decentralized social networking. [1] [2]
History
Mastodon began in 2016 as an open-source project created by Eugen Rochko, with a first public release in October 2016. [3]
In 2025, Mastodon’s CEO and creator announced plans to hand control of the project to a new nonprofit organization, as part of a governance transition intended to reduce reliance on a single individual. [4]
Technology
ActivityPub and federation
Mastodon implements ActivityPub for decentralized social networking. ActivityPub defines both a client-to-server API (for user-facing applications to talk to a server) and a server-to-server API (for servers to federate by exchanging activities such as creating posts or following accounts). [2]
The protocol components map onto Mastodon’s architecture roughly as follows. [2] [5]
| Layer / concept | What it is | How it shows up in Mastodon |
|---|---|---|
| ActivityPub client-to-server | How user-facing apps communicate with a user’s home server | Enables Mastodon web/mobile clients and third‑party apps to perform actions through the user’s instance. [2] |
| ActivityPub server-to-server | How servers federate with other servers by exchanging activities | Instances exchange activities (e.g., posting, following, sharing) so interactions can cross server boundaries. [2] |
| Activities and objects | The “verbs” and “things” sent between parties (e.g., Create, Like, Announce) | Mastodon documents which ActivityPub activities and objects it supports and how they relate to Mastodon features. [5] |
| Instance | An independently run server with its own admins and policies | Users join a chosen instance; federation lets them interact with accounts on other instances. [6] [1] |
Mastodon’s documentation describes how ActivityPub is used in the platform and outlines the specific ActivityPub activities and objects it supports. [5]
Instances
Mastodon is organized as a network of independently operated servers (“instances”). Users create accounts on a chosen instance; their posts and social connections can still reach users on other instances through federation. [1] [6]
Key features
- Community-run servers and local rules: Instances are independently administered and can set their own rules and moderation policies while still interoperating with other servers. [1] [6]
- Open-source ecosystem: Mastodon’s server software is developed as an open-source project, enabling self-hosting and third-party clients through its APIs. [7]
Related standards
While ActivityPub defines federated social networking at the protocol level, other web standards are commonly used in decentralized systems for discovery. For example, WebFinger (RFC 7033) specifies a way to discover information about an account identifier (often expressed as an acct: URI) via HTTPS. [8]
Governance
Mastodon is operated by Mastodon gGmbH, which publishes the official project website and documentation. [1] [6]
Reporting in 2025 described a planned transfer of control to a new nonprofit organization, representing a significant change in how the project is governed. [4]
- ^a ^b ^c ^d ^e Mastodon — Decentralized social media. Mastodon gGmbH. https://joinmastodon.org/.
- ^a ^b ^c ^d ^e ActivityPub. W3C. https://www.w3.org/TR/activitypub/.
- ^ About - Mastodon. Mastodon gGmbH. https://joinmastodon.org/about.
- ^a ^b Preston, Dominic (2025-01-13). Mastodon’s CEO and creator is handing control to a new nonprofit organization. The Verge. The Verge. https://www.theverge.com/2025/1/13/24342603/mastodon-non-profit-ownership-ceo-eugen-rochko.
- ^a ^b ^c What is ActivityPub? Mastodon gGmbH. https://docs.joinmastodon.org/spec/activitypub/.
- ^a ^b ^c ^d Mastodon Documentation. Mastodon gGmbH. https://docs.joinmastodon.org/.
- ^ mastodon/mastodon (GitHub repository). GitHub. https://github.com/mastodon/mastodon.
- ^ Jones, P.; Salgueiro, G.; Jones, M.; Smarr, J. (2013-09). RFC 7033: WebFinger. RFC Editor. https://www.rfc-editor.org/rfc/rfc7033.