Mastodon: posting rules and settings

What a Mastodon channel accepts in Postemi: media, limits, required fields, and the fields of the settings object for the API.

Basics

Rules

• Mastodon has no platform-specific settings. The __type field is enough in the settings object.
• mastodon is an account on mastodon.social; mastodon-custom is an account on any other server, connected with its address.
• Extra parts of a post are published as replies to it, in order.
• Postemi counts 500 characters, the Mastodon default, even where a server allows more.
• Beta: not yet tested with many accounts.

Settings fields

Examples

Each example is one item in the POST /public/v1/posts request's posts array. The envelope around it is always this:

{
  "type": "schedule",
  "date": "2026-09-15T09:00:00.000Z",
  "shortLink": false,
  "posts": [ /* the item below */ ]
}

{
  "integration": { "id": "<channel-id>" },
  "value": [{ "content": "<p>The text of the post.</p>", "image": [] }],
  "settings": { "__type": "mastodon" }
}

The channel ID comes from the channel list, and the path values for images and videos from media upload. The exact schema for the connected account comes from the settings schema endpoint. From the command line, the same thing is the --settings flag. See the CLI examples.