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]

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]