ActivityPub Concepts: JSON-LD, Actor, & IDs

This document covers the fundamental data structures and concepts in ActivityPub.

JSON-LD & Context

ActivityPub objects are JSON-LD documents. They must include the @context property.

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Note",
  "content": "Hello world"
}

Actor

An Actor represents a user, group, organization, or application.

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Person",
  "id": "https://social.example/users/alice",
  "name": "Alice",
  "inbox": "https://social.example/users/alice/inbox",
  "outbox": "https://social.example/users/alice/outbox"
}

ID & URI Structure

Every object in ActivityPub must have a unique, persistent URI (ID).

• https://social.example/users/{username} (Actor)
• https://social.example/users/{username}/outbox (Collection)
• https://social.example/users/{username}/notes/{uuid} (Object)
• https://social.example/users/{username}/activities/{uuid} (Activity)