Mastodon isn’t one website, it’s thousands of servers that talk to each other. Your account lives on one of them, called an instance, and that has one consequence worth knowing before you set up scheduling.
Your instance sets the rules
The commonly quoted 500-character limit is the default, not a law. Instance operators can change it, and some do. Storage limits, media size caps and allowed file types vary the same way.
So the honest answer to “what’s the character limit on Mastodon” is: usually 500, check your instance. If you’re on a large general-purpose server you’re almost certainly on the defaults.
Through BulkPublish, Mastodon is handled with:
| Post length | 500 characters |
| Images | Up to 4, 16 MB each, JPG, PNG, WebP, AVIF, HEIF or GIF |
| Video | Up to 99 MB and 300 seconds, MP4 |
| Threads | Supported |
That image format list is unusually broad, which is a nice side effect of Mastodon being built by people who care about this sort of thing.
Connecting an account
Because there’s no central Mastodon, connecting means telling the tool which instance you’re on. You authorise the app on your own server, and your instance is where the posts go.
If you move instances later, that’s a new connection rather than a settings change, in the same way moving instance is genuinely moving accounts.
Scheduling one
- Connect your account, specifying your instance
- Write the post
- Add media, with alt text
- Pick a date and time
- Queue it
Alt text is worth calling out here specifically. Mastodon’s culture takes image descriptions more seriously than most networks, to the point where posting an image without alt text will get you polite corrections. It’s a norm rather than a rule, and it’s a real one.
Cross-posting to and from Mastodon
Two things to keep in mind, one technical and one social.
Technically it’s easy. Mastodon, Bluesky, Threads and X are close enough in format that one draft covers all four. Mastodon’s 500 characters is the joint-most generous:
| Platform | Limit |
|---|---|
| X | 280 |
| Bluesky | 300 |
| Threads | 500 |
| Mastodon | 500 |
Socially, be careful. Mastodon communities are noticeably less tolerant of accounts that are obviously automated relays. An account that only ever mirrors its posts from elsewhere, never replies, and posts “link in bio” style calls to action will be muted quickly.
Cross-posting to Mastodon is fine. Treating Mastodon as a broadcast target is what gets a cold reception. If you’re going to be there, be there.
Scheduling Mastodon alongside everything else
BulkPublish publishes to Mastodon and 14 other networks: Facebook, Instagram, TikTok, YouTube, X, Threads, Bluesky, Pinterest, Google Business Profile, LinkedIn, Discord, Telegram, Tumblr and Snapchat.
- Channels: Free: 3 (1 per platform). Pro: 30 (2 per platform). Business: 75 (5 per platform).
- Posts: Free: 3/day. Pro: 30/day. Business: unlimited.
The short version
Check your instance’s limits rather than assuming 500 characters, connect by specifying your instance, and always write alt text. Cross-posting from the other short-text networks works well technically. Just don’t make the account a pure relay, because that’s the one thing Mastodon communities reliably dislike.