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GameLink Broadcasts and Subscriptions

GameLink has two related messaging patterns: a game client can broadcast JSON to extension viewers, and it can subscribe to specific GameLink service streams. The pinned source does not define a generic custom-topic WebSocket subscription.

Release status

This page is pinned to untagged public commit 16c6b97; publication remains blocked until a versioned GameLink contract is available.

See GameLink WebSocket Protocol for the common envelope.

Broadcast to viewers

Send action: "broadcast". The request has no service target; its data object contains the developer-defined topic and a nested JSON object named data.

{
  "action": "broadcast",
  "params": {
    "request_id": 20
  },
  "data": {
    "topic": "rare-drop",
    "data": {
      "item": "Thunderfury, Blessed Blade of the Windseeker",
      "player_id": 12345
    }
  }
}

The pinned SDK requires the serialized broadcast value to be under 8 KiB. Its JSON overload documents the nested value as an object, not a primitive or array. An empty broadcast uses "data": {}.

The source does not include an ids allowlist or a message string in this request. Do not add either field to the GameLink broadcast envelope.

Broadcast response

{
  "meta": {
    "request_id": 20,
    "action": "broadcast",
    "target": "",
    "timestamp": 1624574713916
  },
  "data": {
    "ok": true
  }
}

The topic filters messages on the viewer-extension side. It is not a custom WebSocket target that the game client subscribes to.

Service subscriptions

Subscription selectors live in data; params.target selects the GameLink service.

Stream	params.target	Selector in data	Details
Authentication schema event	authentication	No data body	Authentication
State updates	state	topic_id: channel or extension	State access
Poll updates	poll	topic_id: poll ID	Polling
Purchase updates	twitchPurchaseBits	sku: a SKU or *	Purchase transactions

For example, subscribe to one poll as follows:

{
  "action": "subscribe",
  "params": {
    "request_id": 21,
    "target": "poll"
  },
  "data": {
    "topic_id": "favorite-color"
  }
}

Unsubscribe with the same target and selector:

{
  "action": "unsubscribe",
  "params": {
    "request_id": 22,
    "target": "poll"
  },
  "data": {
    "topic_id": "favorite-color"
  }
}

Successful subscription changes use the common { "ok": true } response body. Stream messages arrive in response envelopes with meta.action: "update"; each service page defines its update body and target.