How Mastodon operates as a nonprofit alternative to X

Mastodon, founded in 2016 by Eugen Rochko, is a nonprofit, decentralized microblogging platform that operates as a community-led alternative to centralized social networks. Unlike traditional platforms, Mastodon is built on a federated model. Instead of a single company controlling the entire network, it is composed of individual servers, often called “instances,” which are run by independent individuals, groups, or organizations. These servers connect through ActivityPub, a networking protocol that allows users on different servers to communicate with one another. This interconnected web of independent social media services is known as the “Fediverse.” Individual server administrators set their own moderation policies and rules for sign-ups, meaning some servers are open to anyone while others require approval. When users register, they choose a specific server to host their account, but they remain free to follow and interact with users across different servers.

This decentralized structure positions Mastodon as a distinct, global alternative to mainstream platforms, though its scale remains comparatively small. As of summer 2025, Mastodon has under one million monthly active users and around 10 million registered users. In contrast, its competitor platform X had an estimated 132 million daily active users. While other competitors like Threads support ActivityPub, allowing their users to share posts with Mastodon servers, others are taking different paths. For example, Bluesky is not planning to integrate with ActivityPub, having decided to build its own networking protocol instead.

Because Mastodon is open source, anyone can download, modify, and install its code on their own servers. However, this open nature has occasionally led to friction. Former President Donald Trump’s social media platform, Truth Social, used Mastodon’s code when it launched and “passed it off as if it were original software.”

For users and developers operating within the network, Mastodon supports standard microblogging features like replies, favorites, and hashtags, alongside a quote-tweet feature rolled out in 2025. However, the platform maintains specific technical constraints for media uploads:

• Users can attach up to four images per post.
• Individual images are limited to a maximum size of up to eight megabytes.
• Video and audio files are subject to a strict limit of 40 megabytes.

Why it matters

Mastodon serves as a decentralized, nonprofit alternative to platforms like X, offering a federated network model that prioritizes community-led moderation over centralized control.