Skip to main content

Objects

Objects in ActivityPub represent content — posts, images, videos, events, and more. They're the "things" that activities act upon.

Base Object Properties​

All objects can have these properties:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Note",
  "id": "https://example.com/notes/1",
  "attributedTo": "https://example.com/users/alice",
  "content": "Hello, Fediverse!",
  "published": "2024-01-15T10:30:00Z",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://example.com/users/alice/followers"]
}

Core Properties​

PropertyTypeDescription
typeStringObject type (Note, Article, etc.)
idURLUnique, dereferenceable identifier
attributedToURL/ActorCreator of the object
contentStringMain content (HTML allowed)
publishedDateTimeCreation timestamp
updatedDateTimeLast modification timestamp

Addressing​

PropertyDescription
toPrimary recipients
ccSecondary recipients
btoPrivate primary recipients
bccPrivate secondary recipients

Content Properties​

PropertyDescription
summaryContent warning or preview
contentMapLocalized content {"en": "Hello"}
sourceOriginal source format
mediaTypeMIME type of content

Common Object Types​

Note​

Short-form content (like tweets/toots):

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Note",
  "id": "https://example.com/notes/1",
  "attributedTo": "https://example.com/users/alice",
  "content": "<p>Hello, Fediverse! 👋</p>",
  "published": "2024-01-15T10:30:00Z",
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://example.com/users/alice/followers"],
  "sensitive": false,
  "tag": [],
  "attachment": []
}

Article​

Long-form content (blog posts):

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Article",
  "id": "https://blog.example/posts/1",
  "attributedTo": "https://blog.example/users/writer",
  "name": "My First Blog Post",
  "content": "<p>This is the full content...</p>",
  "summary": "A brief introduction to my blog",
  "published": "2024-01-15T10:30:00Z",
  "url": "https://blog.example/posts/my-first-blog-post"
}

Key difference: Article typically has a name (title), Note does not.

Image​

Photo posts:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Image",
  "id": "https://pixelfed.example/p/1",
  "attributedTo": "https://pixelfed.example/users/photographer",
  "name": "Sunset at the beach",
  "url": {
    "type": "Link",
    "href": "https://pixelfed.example/storage/photos/1.jpg",
    "mediaType": "image/jpeg",
    "width": 1920,
    "height": 1080
  }
}

Video​

Video content:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Video",
  "id": "https://peertube.example/videos/1",
  "attributedTo": "https://peertube.example/accounts/creator",
  "name": "Tutorial: Building with ActivityPub",
  "duration": "PT15M30S",
  "url": [
    {
      "type": "Link",
      "href": "https://peertube.example/videos/1.mp4",
      "mediaType": "video/mp4",
      "height": 1080
    },
    {
      "type": "Link",
      "href": "https://peertube.example/videos/1.webm",
      "mediaType": "video/webm"
    }
  ]
}

Page​

Link shares (like Lemmy posts):

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Page",
  "id": "https://lemmy.example/post/1",
  "attributedTo": "https://lemmy.example/u/alice",
  "name": "Interesting Article About ActivityPub",
  "url": "https://example.com/article",
  "content": "This is my commentary on the article..."
}

Event​

Calendar events:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Event",
  "id": "https://events.example/events/1",
  "name": "Fediverse Developer Meetup",
  "startTime": "2024-02-15T18:00:00Z",
  "endTime": "2024-02-15T21:00:00Z",
  "location": {
    "type": "Place",
    "name": "Community Center",
    "address": "123 Main St"
  }
}

Replies​

Objects can be replies to other objects:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Note",
  "id": "https://example.com/notes/2",
  "attributedTo": "https://example.com/users/bob",
  "content": "Great point!",
  "inReplyTo": "https://other.example/notes/1",
  "to": [
    "https://other.example/users/alice",
    "https://www.w3.org/ns/activitystreams#Public"
  ]
}

Reply Collection​

Posts can link to their replies:

{
  "type": "Note",
  "id": "https://example.com/notes/1",
  "replies": {
    "type": "Collection",
    "id": "https://example.com/notes/1/replies",
    "first": "https://example.com/notes/1/replies?page=1"
  }
}

Media Attachments​

Objects can have media attachments:

{
  "type": "Note",
  "content": "Check out this photo!",
  "attachment": [
    {
      "type": "Document",
      "mediaType": "image/jpeg",
      "url": "https://example.com/media/photo.jpg",
      "name": "A beautiful sunset",
      "blurhash": "LEHV6nWB2yk8pyo0adR*.7kCMdnj",
      "width": 1920,
      "height": 1080
    }
  ]
}

Blurhash​

Mastodon uses blurhash for image placeholders:

{
  "type": "Document",
  "url": "https://example.com/image.jpg",
  "blurhash": "LEHV6nWB2yk8pyo0adR*.7kCMdnj"
}

Tags​

Hashtags​

{
  "type": "Note",
  "content": "<p>Learning about <a href=\"https://example.com/tags/activitypub\">#activitypub</a></p>",
  "tag": [
    {
      "type": "Hashtag",
      "href": "https://example.com/tags/activitypub",
      "name": "#activitypub"
    }
  ]
}

Mentions​

{
  "type": "Note",
  "content": "<p>Hey <a href=\"https://other.example/users/bob\">@bob</a>!</p>",
  "tag": [
    {
      "type": "Mention",
      "href": "https://other.example/users/bob",
      "name": "@bob@other.example"
    }
  ],
  "to": ["https://other.example/users/bob"]
}

Custom Emoji​

{
  "type": "Note",
  "content": "<p>This is awesome :awesome:</p>",
  "tag": [
    {
      "type": "Emoji",
      "id": "https://example.com/emoji/awesome",
      "name": ":awesome:",
      "icon": {
        "type": "Image",
        "url": "https://example.com/emoji/awesome.png",
        "mediaType": "image/png"
      }
    }
  ]
}

Content Warnings​

Use sensitive and summary for content warnings:

{
  "type": "Note",
  "sensitive": true,
  "summary": "Spoilers for the new movie",
  "content": "<p>The ending was amazing when...</p>"
}

Visibility​

Control who can see objects:

Public​

{
  "to": ["https://www.w3.org/ns/activitystreams#Public"],
  "cc": ["https://example.com/users/alice/followers"]
}

Unlisted (Public but not in timelines)​

{
  "to": ["https://example.com/users/alice/followers"],
  "cc": ["https://www.w3.org/ns/activitystreams#Public"]
}

Followers-Only​

{
  "to": ["https://example.com/users/alice/followers"],
  "cc": []
}

Direct Message​

{
  "to": ["https://other.example/users/bob"],
  "cc": []
}

Polls (Question)​

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Question",
  "id": "https://example.com/questions/1",
  "attributedTo": "https://example.com/users/alice",
  "content": "What's your favorite programming language?",
  "endTime": "2024-01-22T10:30:00Z",
  "oneOf": [
    {
      "type": "Note",
      "name": "JavaScript",
      "replies": {
        "type": "Collection",
        "totalItems": 42
      }
    },
    {
      "type": "Note",
      "name": "Python",
      "replies": {
        "type": "Collection",
        "totalItems": 38
      }
    }
  ]
}

Use oneOf for single-choice, anyOf for multiple-choice.

Location​

Adding location to objects:

{
  "type": "Note",
  "content": "Beautiful day at the park!",
  "location": {
    "type": "Place",
    "name": "Central Park",
    "latitude": 40.785091,
    "longitude": -73.968285
  }
}

Object Fetching​

When you receive a reference to an object, you may need to fetch it:

GET /notes/1 HTTP/1.1
Host: example.com
Accept: application/activity+json
tip

Cache fetched objects to reduce network requests. A TTL of 1-24 hours is typical.

Tombstones​

Deleted objects become Tombstones:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Tombstone",
  "id": "https://example.com/notes/1",
  "formerType": "Note",
  "deleted": "2024-01-16T12:00:00Z"
}

Return HTTP 410 Gone for deleted objects.

Next Steps​