What Is Mastodon?

Ask “what is Mastodon?” and the easiest mistake is treating it like one website.

The official project site is joinmastodon.org, but the Mastodon network itself is not one domain with one global database behind it. Mastodon is open-source social networking software that many independent servers can run. Those servers can connect to each other, so an account on one server can follow, mention, reply to, and be followed by accounts on other servers.

Mastodon takes the social network apart into smaller pieces: operators, communities, rules, and software that agree on a shared protocol.

Mastodon is software, not one site

The Mastodon project describes the software as a free, open-source social network server based on ActivityPub. A server can publish text, links, images, audio, video, polls, and other social objects. Users can follow friends and find new accounts much like they would on a familiar microblogging service.

The familiar interface hides the main difference. Mastodon’s own server directory says plainly that Mastodon is not a single website. To use it, you make an account with a provider, and Mastodon calls those providers servers. Older posts and admins often call them “instances”. The words usually mean the same thing in casual Fediverse conversation.

An account name has two parts: the username and the server. @[email protected] identifies Alice’s account on example.org, in the same way an email address belongs to a domain.

That domain matters. The server stores the account, serves the profile, receives posts from other servers, applies local moderation policy, queues background work, stores media, and handles the boring parts users only notice when they break.

What users actually do

From a user’s side, Mastodon looks familiar. You create a profile, post updates, attach media, follow people, reply, boost, favorite, mute, block, and report. Mastodon’s posting documentation says the default character limit is 500 characters, with media attachment support for images, video, audio, and polls. Individual servers and forks can change limits; on July 3, 2026, C.IM’s public instance API reported a 5,000 character post limit.

The home feed feels different from the ranked timelines people are used to elsewhere. Mastodon’s homepage describes a feed with no algorithms or ads and chronological posts from followed accounts. Servers still have arguments, bad posts, and moderation mistakes. The default product is not built around selling ranked attention to advertisers.

For operators, that design choice is not a slogan. A Mastodon server still has costs: compute, object storage, email delivery, moderation time, backups, upgrades, abuse handling, and the occasional weekend spent reading Sidekiq queues while pretending this is a hobby. Removing advertising does not remove the bill. Someone still pays it, usually much closer to the community using the server.

How servers talk to each other

Mastodon federation uses ActivityPub. The W3C ActivityPub Recommendation was published on January 23, 2018, and defines both a client-to-server API and a server-to-server federation protocol for delivering content and notifications.

Email is the easiest comparison. Gmail, Fastmail, Proton Mail, and a self-hosted mail server can exchange messages because they agree on mail protocols. They do not need the same owner, UI, spam filter, storage system, or business model.

Mastodon servers work similarly for social actions. Your account has an ActivityPub actor document with endpoints such as an inbox and an outbox. When you follow someone on another server, your server sends a Follow activity. When that remote account posts, the remote server can deliver a Create activity to your server. Your client then shows the result in your timeline.

Plenty of other software speaks ActivityPub too. PeerTube, Pixelfed, Lemmy, WriteFreely, and other Fediverse projects use the same general protocol family. That is why a Mastodon account can follow a PeerTube channel or interact with posts from non-Mastodon software when both sides support the needed ActivityPub behavior.

Federation is real interoperability, with rough edges. Different software can interpret objects differently. Replies can look incomplete from one server and fuller from another. Some servers block each other. Some servers disappear. The protocol gives the network a common language; operators still have to run the network.

Who makes the rules

Centralized social networks usually have one top-level policy system. Mastodon pushes more of those choices to servers.

Every server is operated by an independent person or organization, and Mastodon’s server directory warns that providers may differ in moderation policies. A small art community, a public institution, a language-specific server, and a personal single-user server do not need the same rules.

Moderation is local by design. Mastodon’s admin documentation says moderation actions are applied locally as seen from a particular server. An admin on one server cannot directly delete a user from another server; they can limit, suspend, or reject that remote account’s local presence. For whole-server problems, Mastodon supports domain blocks with levels such as rejecting media, limiting a server, suspending a server, and importing blocklists.

People often read “decentralized” as “unmoderated”. Mastodon is closer to distributed moderation. Communities get more control, and users get more homework. Choosing a server is closer to choosing an email provider, a neighborhood, and a sysadmin at the same time.

Mastodon’s own promoted server list adds a baseline. Servers listed there commit to the Mastodon Server Covenant, including active moderation against racism, sexism, homophobia and transphobia, daily backups, emergency admin access, and at least three months’ notice before shutdown. That covenant applies to servers Mastodon promotes, not every server on the internet.

How Mastodon is funded

The video script says Mastodon instances are usually crowdfunded. Many are, but the claim is too broad as written.

Mastodon’s documentation is more precise: the software itself does not implement monetization strategies, while server operators may use paid accounts, existing company infrastructure, crowdfunding, or personal funds. The same page says Mastodon development is crowdfunded through Patreon and OpenCollective, and that no venture capital is involved.

Mastodon is not financed by one ad business that owns the whole network. It is also not cost-free. Every server has to solve its own funding, capacity, legal, and moderation problems. Some do that well. Some do it for a while. Some close.

How large is it?

As of July 2, 2026, Mastodon’s public statistics API reported 7,877 servers, 10,357,373 registered users, and 722,073 monthly active users.

The same API shows a modest one-month trend: server count drifted down from roughly 8,030 at the start of June 2026 to 7,877 on July 2, registered accounts rose slightly, and monthly active users moved from the mid-730,000s to 722,073.

There is no single central database of every account on every server, so those figures need careful wording. They are useful, but they are not the same kind of number a centralized platform can produce from one internal analytics database. Public Fediverse statistics depend on reachable servers, reporting behavior, crawling, software compatibility, and duplicate or abandoned accounts. Treat them as a measured public snapshot, not a census.

The older “over a million registered users” line from early Mastodon explainers was true for its time. In 2026, it undersells the registered-account count and overstates our ability to produce one perfect live total.

What decentralization does not promise

Mastodon is harder to capture than a single corporate platform because no one company owns every server, account, timeline, and moderation queue. A company can buy one server. It cannot buy the whole protocol with one acquisition contract.

Your account still depends on your home server. That server can close. A government or network provider can block a domain. An admin can change policy. A storage failure can hurt if backups are bad. A community can split over moderation decisions because communities do that, usually with spreadsheets.

Decentralization changes the failure mode. Instead of one global platform outage, sale, policy change, or API shutdown, the network has many smaller points of failure and many paths around them. Healthier, often. Maintenance-free, no.

For users, the practical rule is simple: choose a server whose policies, funding model, jurisdiction, and admins you can live with. For operators, the rule is less poetic: publish clear rules, patch quickly, keep backups, monitor federation queues, document shutdown policy, and do not pretend moderation is an optional plugin.

Where C.IM fits

C.IM is our Mastodon server. P.LU runs PeerTube for video. R.NF runs Lemmy for discussions. They are separate services, but ActivityPub lets them sit on the same Fediverse map.

A C.IM user can follow people on other Mastodon servers. In many cases, they can also follow compatible accounts or channels from other ActivityPub software. Every app keeps its own shape. The social relationship can still cross the server boundary.

So, what is Mastodon?

It is a social network, but that answer is too small. Mastodon is open-source microblogging software for a federated social web: many servers, many communities, one shared protocol, and no single owner of the whole conversation.