documentation/content/en/development/activitypub.md

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ActivityPub compliance	What objects and properties of the ActivityPub spec Mastodon supports	docs parent weight development 5

APIs

• Mastodon supports the server-to-server part of the ActivityPub spec.
• It implements the HTTP signatures spec for authentication of inbox deliveries.
• Mastodon also supports Linked Data Signatures for forwarded payloads.

Restrictions

• Mastodon requires all object IDs to use the HTTPS schema.
• Mastodon also requires servers to offer a WebFinger endpoint for converting username/domain pairs into actors.
• Mastodon accepts Application, Group, Organization, Person, and Service as valid types for actors.
• Mastodon requires activities attributed to an actor to have an ID on the same host as the actor.

Activities

Supported activity	Supported objects	Notes
Accept	Follow	The object of the Follow is expected to be an actor from the receiving server
Add	Note	Only the actor's own objects and only to the actor's featured collection URI as target
Announce	Object	Any object supported by Create is supported here
Block	Object	The object is expected to point to an actor from the receiving server
Create	Note, Article, Image, Video
Delete	Object	Only the actor's own objects will be deleted, such as anything created before
Flag	Object	The object is expected to point to one or multiple objects originating on the receiving server
Follow	Object	The object is expected to point to an actor from the receiving server
Like	Object	The object is expected to be something created on the receiving server
Move	Object	Only the actor's own actor object can be moved to another actor object at target
Reject	Follow	The object of the Follow is expected to be an actor from the receiving server
Remove	Note	Only the actor's own objects and only from the actor's featured collection URI as origin
Undo	Accept, Announce, Block, Follow, Like
Update	Object	Only the actor's own actor object can be updated

Extensions

Featured collection

What is known in Mastodon as "pinned toots", or statuses that are always featured at the top of people's profiles, is implemented using an extra property featured on the actor object that points to a Collection of objects. Example:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
        
    {
      "toot": "http://joinmastodon.org/ns#",
      "featured": {
        "@id": "toot:featured",
        "@type": "@id"
      }
    }
  ],

  "id": "https://example.com/@alice",
  "type": "Person",
  "featured": "https://example.com/@alice/collections/featured"
}

Custom emojis

Mastodon supports arbitrary emojis, that is, small images uploaded by admins and invokable via shortcodes. For this, an Emoji type is used. These emojis are listed in the tag property just like Mention and Hashtag objects, since they are entities that affect how the text is rendered. Example:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
        
    {
      "toot": "http://joinmastodon.org/ns#",
      "Emoji": "toot:Emoji"
    }
  ],

  "id": "https://example.com/@alice/hello-world",
  "type": "Note",
  "content": "Hello world :Kappa:",
  "tag": [
    {
      "id": "https://example.com/emoji/123",
      "type": "Emoji",
      "name": ":Kappa:",
      "icon": {
        "type": "Image",
        "mediaType": "image/png",
        "url": "https://example.com/files/kappa.png"
      }
    }
  ]
}

Focal points

Mastodon supports setting a focal point on uploaded images, so that wherever that image is displayed, the focal point stays in view. This is implemented using an extra property focalPoint on the Image objects. The property is simply an array of two floating points between 0 and 1. Example:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
        
    {
      "toot": "http://joinmastodon.org/ns#",
      "focalPoint": {
        "@container": "@list",
        "@id": "toot:focalPoint"
      }
    }
  ],

  "id": "https://example.com/@alice/hello-world",
  "type": "Note",
  "content": "A picture attached!",
  "attachment": [
    {
      "type": "Image",
      "mediaType": "image/png",
      "url": "https://example.com/files/cats.png",
      "focalPoint": [
        0.55,
        0.43
      ]
    }
  ]
}