Mastodon is a free, open-source, self-hosted social network server built on ActivityPub that lets anyone run a microblogging community which interoperates with the wider Fediverse, and it is aimed at individuals, communities, and organisations that want to own their social graph instead of renting it from a platform.

What it is

Mastodon is a social network server written in Ruby on Rails under the AGPL-3.0 licence, first released in 2016 and maintained by Eugen Rochko together with the mastodon authors. It implements the ActivityPub protocol and WebFinger for discovery, so a server does not form an island: users on one instance follow and communicate with users on other instances, including software that is not Mastodon but still speaks ActivityPub. Users can publish links, pictures, text, and video, and every server on the network is interoperable as part of a federated whole known as the Fediverse.

The concrete problem it solves is vendor lock-in and the loss of control that comes with a centrally operated social account. Where a hosted microblogging service owns the account, the audience, and the data, Mastodon moves all three onto infrastructure the operator controls, with no vendor lock-in and no dependency on a single company's terms of service. The software itself replaces the closed, centrally hosted microblogging platform: the timeline, the follow graph, the media attachments, and the moderation decisions all live on a server that its own administrators run.

Key capabilities

• ActivityPub federation, so users on one server can follow and interact with users on other servers, including non-Mastodon implementations of the same protocol.
• WebFinger for account discovery across instances and ActivityStreams-style data exchange across the Fediverse.
• Real-time, chronological timeline updates, where posts from followed accounts appear immediately in the user interface.
• Media attachments for images and videos, with silent videos treated like animated GIFs and normal videos looping continuously.
• Safety and moderation tooling including private posts, locked accounts, phrase filtering, muting, blocking, reporting, and a moderation system.
• An OAuth2 provider role plus a straightforward REST API and a Streaming API, which support a broad third-party app ecosystem.
• An official container image published as mastodon under the GitHub container registry, alongside Docker and docker-compose deployment configurations in the repository.

Who uses it and how

• Community and organisational server operators who run their own instance so that their members' posts, follows, and media stay on their own infrastructure.
• Administrators who deploy with the repository's Docker and docker-compose configurations, or with the provided configurations for Heroku and Scalingo, and who use the Helm charts from the mastodon/chart repository for Kubernetes.
• Moderators who rely on the built-in reporting and moderation system, private posts, locked accounts, and phrase filtering to keep a server's local timeline in order.
• Application developers who build third-party clients against the OAuth2, REST, and Streaming APIs rather than the web interface.
• Federated users who follow and interact with accounts on other instances, including servers running different ActivityPub software.

Getting started

Deployment is handled either through the official container image at github.com/mastodon/mastodon/pkgs/container/mastodon, through the in-repository Docker and docker-compose configurations, or through the standalone installation guide in the project documentation at docs.joinmastodon.org/admin/install/.

How it compares

No list of paid products that this project replaces is provided in the facts, and no comparable projects are named by name there either, so Mastodon stands alone in this registry as the ActivityPub-based microblogging server it is. What the facts do establish is that its interoperability extends beyond itself, since any software implementing ActivityPub joins the same broader social network.

When to use it — and when not to

A self-hoster must operate the full stack, which means Ruby 3.3 or newer, PostgreSQL 14 or newer, Redis 7.0 or newer, Node.js 22 or newer, FFmpeg 5.1 or newer, and the Sidekiq queueing and caching layer that the streaming API depends on. Anyone who wants zero operational work, or who has no appetite for running a database and a queue in production, should not pick it; the same applies to groups unwilling to take on moderation duties. The visible weakness is maintenance load at the project level: 4525 open issues sit against 7498 forks and 50298 stars, which signals both a large contributor base and a backlog that self-hosters may end up resolving on their own.

Copyright (c) 2016-2026 Eugen Rochko & other Mastodon contributors

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Affero General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your option) any
later version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
details.

You should have received a copy of the GNU Affero General Public License along
with this program. If not, see https://www.gnu.org/licenses/