Mastodon (social network)

Mastodon is a free and open-source, decentralized microblogging social network built around federation: independent servers (“instances”) interoperate to form a larger network often referred to as the fediverse. The fediverse is not limited to microblogging; it also includes other ActivityPub-connected services such as the photo-sharing platform Pixelfed and the video platform PeerTube. ^{[1] [2] [3]}

Mastodon uses the ActivityPub protocol primarily for server-to-server federation, while user-facing clients typically communicate with a user’s home server through Mastodon’s own client API. ^{[4] [5]}

After changes at X (formerly Twitter), Mastodon became a prominent destination in several “Twitter migration” waves, alongside other alternatives. Reporting and research describe rapid influxes of new users followed by retention challenges, as well as a pattern of partial migration in which many users maintain accounts on multiple platforms. ^{[6] [7] [8] [9]}

History

Mastodon began in 2016 as an open-source project created by Eugen Rochko, with a first public release in October 2016. ^[10]

In 2025, Rochko 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. ^[11]

Impact and adoption

Mastodon’s growth has often been tied to periods of upheaval on larger platforms. TechCrunch’s coverage of Mastodon’s annual reporting described a sharp rise in donations and reported monthly active user milestones during the post-Twitter-acquisition period. ^[6]

Beyond individual users, reporting has also framed Mastodon as an emerging piece of public-interest communications infrastructure: Tech.eu reported that Mastodon has turned partnerships into paid services, including arrangements related to institutional hosting/support. ^[12]

Who uses it and migration dynamics

Academic research on the Twitter-to-Mastodon migration describes an “unfinished” transition in which many users straddle both platforms rather than fully switching, emphasizing the role of network effects and the costs of rebuilding social connections across instances. ^[8]

A separate Scientific Reports study analyzed the #TwitterMigration discourse and the sharing of Mastodon identifiers as migration signals, providing an empirical view of how users announced and coordinated movement to Mastodon during migration waves. ^[9]

Technology

ActivityPub and federation

Mastodon implements ActivityPub for decentralized social networking. ActivityPub defines both a client-to-server API and a server-to-server API (for federation). ^[4]

In Mastodon, ActivityPub is primarily used for server-to-server federation; Mastodon clients generally interact with their home server using Mastodon’s own client API rather than ActivityPub’s client-to-server interface. ^{[5] [13]}

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] [14]}

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] [14]}
• Open-source ecosystem: Mastodon’s server software is developed as an open-source project, enabling self-hosting and third-party clients through its APIs. ^[15]

Critiques and challenges

Reporting has described a “bump then slump” pattern in which surges of new users strained volunteer-run infrastructure and moderation capacity, followed by lower activity as some newcomers bounced off onboarding friction and the complexities of choosing and navigating instances. ^[7]

More broadly, the decentralized social web places significant trust-and-safety responsibilities on instance operators and volunteer moderators. IFTAS’ 2025 Social Web Trust & Safety Report (announced in early 2026) highlighted moderator workload, limited tooling, and safety threats as persistent challenges for the ecosystem. ^[16]

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. ^[17]

Governance

Mastodon is operated by Mastodon gGmbH, which publishes the official project website and documentation. ^{[1] [14]}

Reporting in 2025 described a planned transfer of control to a new nonprofit organization, representing a significant change in how the project is governed. ^[11]