Fediverse

The fediverse (short for "federated universe") is the name for all the websites that can communicate with each other over ActivityPub, an open protocol, and the web. Mastodon's documentation defines it that way. Every Mastodon server is part of it, and so is other software that speaks ActivityPub, such as Pixelfed for sharing images, PeerTube for video and Misskey for microblogging.

How Federation Works

Mastodon's documentation compares federation to email. You can send an email from a Gmail account to someone on Outlook as long as you know their address, and in the same way you can mention or message anyone on any Mastodon website by their address. Each website runs on its own, with its own people and rules, and the websites talk to each other.

An address has two parts, the username and the domain of the server, like an email address, for example @alice@example.com. People on the same server can leave out the domain, so when you share your address with anyone else, include it.

Example

An illustrative case (the people and the servers are made up): Alice has an account on example.social, so her address is @alice@example.social. Ben runs a server of his own at ben.example. Ben follows Alice from his server, sees her posts in his home feed and replies to them, and Alice sees his replies. Neither of them needs an account on the other's server.

Fediverse or Mastodon?

The fediverse has no brand of its own. Mastodon's documentation notes that people more often say "follow me on Mastodon" than "follow me on the fediverse", and that the second is technically more correct.

Where Bluesky Fits

Bluesky runs on a different protocol, the AT Protocol, which its own documentation also describes as federated, with account data stored on host servers. Each account has a handle in the form of a domain name. The fediverse, as Mastodon's documentation defines it, is the websites that speak ActivityPub.

Mastodon in Postopus

Postopus publishes to Mastodon. You connect the account on your own Mastodon server, and the editor counts against that server's character limit. The same post can go to LinkedIn, X and Bluesky too, with one text or a version for each.

Sources

Checked on October 27, 2026.

• Mastodon documentation, What is Mastodon?: federation, the email comparison, ActivityPub, the definition of the fediverse and the software that is part of it.
• Mastodon documentation, Signing up for an account: an address is a username plus the server's domain.
• Mastodon documentation, Running your own server: following and being followed across servers.
• AT Protocol, Protocol Overview: handles, DIDs and the federated architecture.

Last reviewed: October 27, 2026