Mastodon is thousands of servers rather than one, and each sets its own rules, which is why a scheduler that holds one number for the whole network gets Mastodon wrong. Preflight registers itself on your instance, reads the instance's own limit when you connect, and publishes text, pictures, video and threads with the visibility, content warning and language Mastodon's own composer offers. How to schedule Mastodon posts covers the workflow; this page is the integration.
| Mastodon through Preflight | What the API allows |
|---|---|
| Text limit | 500 characters |
| Media | Pictures and video, up to 4 files |
| Pictures | Up to 16 MB each |
| Video | 99 MB, no limit enforced |
| Thread in one go | Yes |
| First comment | No |
| Alt text | Yes |
| Edit after publishing | Yes |
| Delete from Preflight | Yes |
| Comments | Read and reply |
| Figures reported | likes, comments, shares |
| Retention and traffic sources | No |
What goes out
A post with up to four pictures or one video, each with alt text; a visibility of public, unlisted, followers only or direct; a content warning, which hides the text and the media behind it; a language tag; a sensitive flag on the media; and a thread, posted as replies under the first post in one go.
Connecting an account
Enter your instance's address. Preflight registers an application on that instance once and reuses it for everyone who connects there, then sends you to the instance's own consent screen for read and write access. The server's character limit is read from the instance at that moment and kept with the account, so a server that allows 5,000 characters is judged at 5,000 and the common 500 is only the default where nothing else is known.
What is checked before publishing
Text against your instance's limit, counted the way Mastodon counts: a link is 23 characters and the domain of a mention is free. A content warning counts toward the same limit, and the two are measured together. Pictures up to 16 MB and video up to 99 MB, mainline Mastodon's defaults; a server with its own ceilings refuses with its own message, which is shown as is. Pictures and a video together are refused, because Mastodon refuses them. More than four files are warned about as dropped. Every part of a thread is measured.
What the API will not do
Almost nothing. Mastodon is the one network here with a real edit endpoint, which changes a published post and keeps its replies and boosts, and a delete. Replies are read, answered and favourited; nothing hides another server's reply, so there is no hide. Figures come back for favourites, replies and boosts. There is no first comment, but the second part of a thread serves. Mastodon can schedule natively too, one post at a time on one instance; a scheduler earns its place when the same post also goes to Bluesky and Threads.
In the API
Visibility, content warning, language, sensitive and threads are fields in the public API and parameters in the MCP server; the instance's limit applies to both. Mastodon is on every plan at pricing.
Questions people ask
- Which Mastodon instances does Preflight support?
- Any that runs the standard Mastodon API, including large ones and your own. Preflight registers itself on the instance the first time someone connects there and reads the server's own character limit.
- Why does my Mastodon post count differently from the composer?
- Mastodon counts a link as 23 characters whatever its length and does not count the domain of a mention; Preflight counts the same way, and a content warning is counted toward the limit as well.
- Can I edit a Mastodon post after publishing?
- Yes. Mastodon's API edits a published post in place, keeping its replies and boosts, so a correction from Preflight does not mean deleting and reposting.