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Connection

Connect to the Gemini WebSocket endpoint: 
wss://api.delphiterminal.co/ws/gemi?api_key=YOUR_API_KEY
PropertyValue
ProtocolWebSocket (wss://)
Authenticationapi_key query parameter
KeepalivePing every 54 seconds
Timeout60 seconds without pong
Max Message Size16 KB

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Subscribing to markets

Once connected, send a JSON message to subscribe using market_id: 
{
  "action": "subscribe",
  "market_ids": ["GEMI-BTC15M-HI70000", "GEMI-FEDJAN26-DN25"],
  "message_types": ["prices", "orderbook", "trades"]
}
FieldTypeRequiredDescription
actionstringYessubscribe or unsubscribe
market_idsarrayYesArray of Gemini market identifiers
message_typesarrayNo["prices"], ["orderbook"], ["trades"], or any combination. Defaults to prices and orderbook if omitted

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Unsubscribing

{
  "action": "unsubscribe",
  "market_ids": ["GEMI-BTC15M-HI70000"]
}

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Message types

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Price messages

{
  "type": "prices",
  "data": {
    "venue": "GEMI",
    "market_id": "GEMI-BTC15M-HI70000",
    "server_time": 1774762511552,
    "ingest_time": 1774762511553,
    "payload": {
      "type": "Ticker",
      "Ticker": {
        "best_bid": 0.45,
        "best_bid_qty": 100,
        "best_ask": 0.55,
        "best_ask_qty": 80
      }
    }
  }
}

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Orderbook messages

{
  "type": "orderbook",
  "data": {
    "exchange": "GEMI",
    "market_id": "GEMI-BTC15M-HI70000",
    "yes_side": [0, 0, 100, 200],
    "no_side": [150, 100, 0, 0],
    "server_time": "2026-03-29T12:00:00Z"
  }
}

​
Trade messages

{
  "type": "trades",
  "data": {
    "venue": "GEMI",
    "market_id": "GEMI-BTC15M-HI70000",
    "server_time": 1774762511552,
    "payload": {
      "type": "Trade",
      "Trade": {
        "trade_id": 12345,
        "price": 0.50,
        "quantity": 100,
        "is_maker": false
      }
    }
  }
}

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Full example

const ws = new WebSocket("wss://api.delphiterminal.co/ws/gemi?api_key=YOUR_API_KEY");

ws.onopen = () => {
  console.log("Connected to Gemini WebSocket");

  ws.send(JSON.stringify({
    action: "subscribe",
    market_ids: ["GEMI-BTC15M-HI70000"],
    message_types: ["prices", "orderbook", "trades"]
  }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);

  if (data.type === "prices") {
    console.log("Price update:", data.data);
  } else if (data.type === "orderbook") {
    console.log("Orderbook update:", data.data);
  } else if (data.type === "trades") {
    console.log("Trade:", data.data);
  }
};

ws.onclose = () => console.log("Disconnected");
ws.onerror = (error) => console.error("WebSocket error:", error);

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Important notes

  • Authentication required via api_key query parameter
  • Use market_id (Gemini market identifier) to subscribe
  • Messages are only sent for markets you have explicitly subscribed to
  • Multiple markets can be subscribed in a single message
  • Trades must be explicitly requested (not included in the default subscription)