> ## Documentation Index
> Fetch the complete documentation index at: https://docs.delphimarkets.com/llms.txt
> Use this file to discover all available pages before exploring further.

# PredictIt WebSocket

> Real-time price streaming for PredictIt prediction markets

## Connection

Connect to the PredictIt WebSocket endpoint:

```
wss://api.delphiterminal.co/ws/prdi?api_key=YOUR_API_KEY
```

| Property         | Value                     |
| ---------------- | ------------------------- |
| Protocol         | WebSocket (wss\://)       |
| Authentication   | `api_key` query parameter |
| Keepalive        | Ping every 54 seconds     |
| Timeout          | 60 seconds without pong   |
| Max Message Size | 16 KB                     |

## Subscribing to markets

Once connected, send a JSON message to subscribe using `market_id`:

```json theme={"theme":"one-dark-pro"}
{
  "action": "subscribe",
  "market_ids": ["34256"],
  "message_types": ["prices"]
}
```

| Field           | Type   | Required | Description                                                                             |
| --------------- | ------ | -------- | --------------------------------------------------------------------------------------- |
| `action`        | string | Yes      | `subscribe` or `unsubscribe`                                                            |
| `market_ids`    | array  | Yes      | Array of PredictIt market identifiers (numeric strings)                                 |
| `message_types` | array  | No       | `["prices"]` only. Defaults to prices if omitted. **No orderbook or trades available.** |

## Unsubscribing

```json theme={"theme":"one-dark-pro"}
{
  "action": "unsubscribe",
  "market_ids": ["34256"]
}
```

## Message types

### Price messages

```json theme={"theme":"one-dark-pro"}
{
  "type": "prices",
  "data": {
    "venue": "PRDI",
    "market_id": "34256",
    "server_time": 1774762511552,
    "ingest_time": 1774762511553,
    "payload": {
      "type": "Ticker",
      "Ticker": {
        "price": 0.42,
        "yes_bid": 0.41,
        "yes_ask": 0.43,
        "volume": 0,
        "open_interest": 0
      }
    }
  }
}
```

## Full example

```javascript theme={"theme":"one-dark-pro"}
const ws = new WebSocket("wss://api.delphiterminal.co/ws/prdi?api_key=YOUR_API_KEY");

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

  ws.send(JSON.stringify({
    action: "subscribe",
    market_ids: ["34256"],
    message_types: ["prices"]
  }));
};

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

  if (data.type === "prices") {
    console.log("Price update:", data.data);
  }
};

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

## Important notes

* **Authentication required** via `api_key` query parameter
* **Prices only** — PredictIt does not provide orderbook depth or individual trade history
* PredictIt data is sourced via REST polling (60-second intervals)
* Only emits updates when market state changes (last trade price, best bid/ask)
* Use `market_id` (PredictIt market identifier) to subscribe