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

# Message Format

> Overview of WebSocket message types and structure.

All WebSocket messages are exchanged as JSON objects.

Every message includes an `op` field that identifies the operation or message type.

The optional `req_id` field can be used to correlate client requests with their corresponding server responses.

***

## Client → Server

| Operation      | Purpose                                                  |
| -------------- | -------------------------------------------------------- |
| `auth`         | Authenticate using a JWT access token                    |
| `auth_api_key` | Authenticate using an API key                            |
| `subscribe`    | Subscribe to one or more topics                          |
| `unsubscribe`  | Unsubscribe from one or more topics                      |
| `ping`         | Keep the connection alive and measure round-trip latency |

Example:

```json theme={null}
{
  "op": "subscribe",
  "args": ["ticker.BTC-USDCx"],
  "req_id": "2"
}
```

***

## Server → Client

| Operation      | Purpose                      |
| -------------- | ---------------------------- |
| `auth`         | Authentication result        |
| `subscribed`   | Subscription confirmation    |
| `unsubscribed` | Unsubscription confirmation  |
| `pong`         | Response to a `ping` message |
| `error`        | Error response               |
| `event`        | Real-time event payload      |

***

## Event Envelope

All streaming updates are delivered using the following envelope:

```json theme={null}
{
  "op": "event",
  "server_ts_ms": 1700000000000,
  "topic": "ticker.BTC-USDCx",
  "data": {}
}
```

Order book events may also include a type field (snapshot vs delta). See the **Public WebSocket Reference** and **Private WebSocket Reference** for complete message schemas and payload definitions.