> For the complete documentation index, see [llms.txt](https://docs.nexus.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nexus.xyz/exchange/apis-and-rates/exchange-websocket.md).

# Exchange Websocket

The WebSocket API delivers real-time order book updates, trades, candles, engine status, and account events (orders, fills, positions, balances, liquidations). It is the recommended path for any latency-sensitive integration.

### Connecting

Browsers cannot attach custom auth headers to a WebSocket upgrade, so authentication uses a short-lived token rather than a header:

1. Call `POST /ws-tokens` over HMAC (a normal signed REST request). This mints a **60-second, single-use** opaque token. Your HMAC secret never crosses the WebSocket boundary.
2. Open a WebSocket to the `/stream` endpoint and present the token to subscribe.

Tokens are single-use and reaped after 60 seconds; mint a fresh one per connection.

### Connection limits

* Maximum **5 active connections per IP**, applied at upgrade time on every tier. A 6th connection is rejected with `HTTP 429` on the upgrade — nothing is evicted, and the single-use token is spent, so mint a fresh one before retrying.
* A per-account connection cap applies on top of that: **5** at the Pro tier, **100** at MarketMaker.
* Subscriptions are capped per connection *and* per account at the same number (Pro 50, MarketMaker 1,000), so more sockets do not buy more subscriptions.
* Inbound client frames are limited per connection (Pro 10/s, MarketMaker 50/s) with a 2× burst; sustained flooding closes the connection with code `1008`.
* **These ceilings are their own budget** — independent of the REST request budget and of the trading-action budget, not shared with them. See [Rate Limits](/interfaces/rate-limits.md).

### Channels

Subscriptions are per-market where noted. Available channels:

| Channel        | Scope      | Payload                      |
| -------------- | ---------- | ---------------------------- |
| `book`         | per market | Order book depth updates     |
| `trades`       | per market | Executed trades              |
| `candles`      | per market | OHLCV candles                |
| `engine`       | global     | Engine throughput and status |
| `orders`       | account    | Order lifecycle updates      |
| `fills`        | account    | Your executed fills          |
| `positions`    | account    | Position changes             |
| `balances`     | account    | Balance changes              |
| `liquidations` | account    | Liquidation events           |

Account-scoped channels (`orders`, `fills`, `positions`, `balances`, `liquidations`) require an authenticated subscription tied to your token.

### Delivery targets

The system targets low-latency fan-out; published latency goals tighten across release gates (order-book and fill delivery measured from the matching event to client receipt). Current testnet behavior is suitable for development and integration testing.

> **Status:** testnet preview. Exact subscription message framing and per-channel schemas are defined in the OpenAPI spec at `/openapi.json` and the live API reference at [exchange.nexus.xyz](https://exchange.nexus.xyz); use those as the authoritative source for message shapes.


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