Broadcast Messaging

Muxy broadcast endpoints publish developer-defined JSON to Twitch Extension PubSub. All three endpoints use POST and the standard Authorization: <Client ID> <JWT> header.

Limits and delivery

Messages at or above 5 KiB are compressed and Base64 encoded, then split into fragments small enough for Twitch PubSub. The compressed, encoded payload must not exceed 80 KiB. Keep messages much smaller when possible and store durable data in state or configuration instead.

Sandbox and production broadcasts are isolated. Delivery is real time but not a durable queue; consumers must tolerate reconnects and missed messages.

Send to a channel

POST /v1/e/broadcast accepts broadcaster, admin, or backend JWTs.

curl --request POST \
  --url https://api.muxy.io/v1/e/broadcast \
  --header "Authorization: ${MUXY_CLIENT_ID} ${MUXY_JWT}" \
  --header 'content-type: application/json' \
  --data '{
    "target": "broadcast",
    "event": "score-updated",
    "user_id": "12345678",
    "data": { "score": 42 }
  }'

Field	Meaning
target	broadcast for everyone on the channel or whisper-U<opaque-user-id> for one viewer
event	Developer-defined event name; defaults to default when omitted
user_id	Twitch channel/broadcaster ID
data	JSON object delivered to subscribers

Send extension-wide

POST /v1/e/extension_broadcast requires a privileged broadcaster, admin, or backend JWT and queues the message for every active channel using the extension.

curl --request POST \
  --url https://api.muxy.io/v1/e/extension_broadcast \
  --header "Authorization: ${MUXY_CLIENT_ID} ${MUXY_JWT}" \
  --header 'content-type: application/json' \
  --data '{
    "event": "catalog-updated",
    "data": { "revision": 7 }
  }'

Send to the current viewer

POST /v1/e/whisper_self sends a back-channel message to the same authorized viewer context. It is useful for coordinating multiple surfaces of one extension.

curl --request POST \
  --url https://api.muxy.io/v1/e/whisper_self \
  --header "Authorization: ${MUXY_CLIENT_ID} ${MUXY_JWT}" \
  --header 'content-type: application/json' \
  --data '{
    "event": "settings-saved",
    "data": { "ok": true }
  }'

Successful requests return HTTP 200. Treat any non-2xx response as undelivered and apply bounded retry logic only where duplicate messages are safe.

See GameLink event handling for subscription callbacks.