A very incomplete description of Facebook's GraphQL schema (from 2017)

incomplete-facebook-schema.graphql

schema {
    Query: Query
    Mutation: Mutation
}

type Query() {
  viewer: Viewer!
  entities_named: SearchableEntitiesQuery!
}

type Viewer() {
    message_threads: ViewerMessageThreadsConnection
}

type ViewerMessageThreadsConnection {
    nodes: [MessageThread!]!
    edges: ViewerMessageThreadsEdge!
    has_next_page: Boolean!
    has_previous_page: Boolean!
}

type ViewerMessageThreadsEdge {
    node: [MessageThread!]!
    cursor: ID!
}

type SearchableEntitiesQuery() {
    search_results: SearchableResultsConnection
}

type SearchableResultsConnection {
    nodes: [Searchable!]!
    edges: SearchableResultsEdge!
    has_next_page: Boolean!
    has_previous_page: Boolean!
}

type SearchableResultsEdge {
    node: [Searchable!]!
    cursor: ID!
}

type Searchable {
    # One of User, MessageThread, Page or Group
}

type User {
    name: String!
    id: Int!
}

type MessageThread {
    name: String
    thread_key: MessageThreadKey
    image:
    is_group_thread:
    all_participants {
        nodes {
            messaging_actor {
                @User
            }
        }
    }
    other_participants:
}

type MessageThreadKey {
    thread_fbid: String
    other_user_id: Int
    legacy_thread_id: String
}

type MessageThreadImage {
    thread_fbid: Int
    ohter_user_id: Int
}

type UserMessage {

}