Mastodon Character Limit: 500 by Default, But Every Server Can Change It

Mastodon's default post limit is 500 characters, according to Mastodon's own documentation — nearly double the original Twitter limit, and enough room for a full thought without needing a reply thread. That number covers the main text field of a post, sometimes called a "toot" in older Mastodon terminology. But the word "default" is doing real work in that sentence, and it's the reason this platform doesn't have a single, universal answer the way a centralized app does.

Why There's No Single Mastodon Character Limit

Mastodon isn't a single company running one website — it's open-source software that anyone can install on their own server, called an instance. Each instance is run by its own admin, who can change the post character limit by editing a single value in the server's configuration (technically, the MAX_CHARS constant in a file called status_length_validator.rb). That means the 500-character figure is the number Mastodon ships with, not a hard ceiling the network enforces everywhere.

In practice, the overwhelming majority of instances — including mastodon.social, the largest and original server — keep the default 500-character limit. But smaller or special-interest instances sometimes raise it: some technical or writing-focused communities run limits in the thousands, and a handful of forks of the Mastodon software go further still. If you want to know the exact limit for the account you're actually posting from, every instance exposes it publicly at /api/v1/instance under configuration.statuses.max_characters — that's the one number worth trusting over any general list, including this one.

How Links and Mentions Are Counted

Two counting rules apply regardless of which instance you're on, and both come straight from Mastodon's own documentation. Any link in a post is counted as exactly 23 characters, no matter how long the actual URL is — which means, unlike on some platforms, there's no benefit to running a link through a shortener before posting; Mastodon's own docs actively discourage it. Mentions work differently from what people expect too: when you type out a full address like @alice@example.com, only the username portion — alice — counts against your character limit. The domain after the second @ is free.

The 500-character default isn't an arbitrary product decision handed down from a single company — it's a starting value in open-source code that any server operator can change. Whether your real limit is 500 or something else entirely depends on which of Mastodon's thousands of independent servers your account happens to live on.

Profile Fields: Display Name, Bio, and Metadata

Outside of individual posts, Mastodon's documentation lists a default 30-character limit for a display name and a 500-character limit for a bio, with the same link-counts-as-23-characters rule applying inside the bio too. Beyond that, profiles also get four customizable metadata rows — label-and-value pairs like "Pronouns: he/him" or "Website: example.com" — but Mastodon's documentation doesn't publish a specific character cap for those fields, so it's fair to say that limit either isn't fixed or isn't publicly documented, rather than guess at a number.

Polls Have Their Own, Smaller Limit

Attaching a poll to a post follows a separate set of rules: up to 4 choices, with each choice limited to 25 characters according to Mastodon's current user-facing documentation. It's worth flagging that this is one spot where sources disagree — Mastodon's own API reference documentation, in an example response that appears to be older, shows a 50-character-per-option field instead. Where the live user-facing docs and an older cached API example conflict, the more recently updated user documentation is the safer number to plan around, but if a poll rejects text you expected to fit, that's the likely reason why.

How Mastodon's Limit Compares to Other Federated and Text-First Platforms

Mastodon's 500-character default sits in the middle of the pack among short-form text platforms, and its refusal to shorten links is actually the more distinctive design choice. Compared with platforms already covered in this series:

The practical effect: a post that fits comfortably on Threads or a default Mastodon instance can still overflow Bluesky, and a post packed with links behaves differently on X — where the shortener keeps every link at a flat 23 characters no matter what you paste in — than it does on Mastodon, where that same 23-character count applies but is explicitly presented as a reason not to bother shortening links at all. For anyone cross-posting the same message to several of these platforms at once, as covered in the broader character limits by platform overview, Mastodon's link rule is one less thing to worry about — but its per-instance variability is one more.

The Fastest Way to Know Your Real Limit

Every number in this post is Mastodon's own documented default, not a guarantee for any specific account. If a post is bouncing at a number that doesn't match what's written here, the instance it's being posted from almost certainly has a custom limit set by its admin — checking that server's /api/v1/instance endpoint settles it in seconds. Outside of that instance-by-instance variable, the fastest way to know exactly how much room is left in a draft — for Mastodon or anywhere else — is to paste it into an actual counter rather than estimate. Clear Count gives an instant character and word count with nothing uploaded anywhere.

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Mastodon's honest answer is: 500 characters per post by default, 30 for a display name, 500 for a bio, and 25 per poll choice — all set by the open-source software itself, and all changeable by whichever server an account happens to live on. That federated structure is Mastodon's defining trait, and it's exactly why "what's the Mastodon character limit" doesn't have quite the same single, fixed answer that it does on a centralized platform.