> ## Documentation Index
> Fetch the complete documentation index at: https://kraken-sandbox.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Choose your protocol

> REST, WebSocket, and FIX — differences, trade-offs, and when to use each

Kraken's Spot and Derivatives markets run on **separate trading engines**, each with its own endpoints and latency characteristics. The right protocol combination depends on which market you trade.

<Tabs>
  <Tab title="Spot">
    Spot offers three protocols. They share the same rate limit counter — choose based on your latency requirements and feature needs.

    |                       |       REST       |     WebSocket    |     Unified FIX     |
    | :-------------------- | :--------------: | :--------------: | :-----------------: |
    | Connection model      | Request/response |    Persistent    |  Persistent session |
    | Latency profile       | Higher, variable |        Low       | Lowest (colocation) |
    | Market data           |         ✅        |         ✅        |          ✅          |
    | Order entry           |         ✅        |         ✅        |          ✅          |
    | Account data          |         ✅        |         ✅        |          —          |
    | L3 order book         |         ✅        |    ✅ (v2 only)   |          ✅          |
    | Order amend           |         ✅        |         ✅        |    ✅ (MsgType=G)    |
    | Cancel on disconnect  |         —        |         —        |          ✅          |
    | FIX message replay    |         —        |         —        |          ✅          |
    | Funding / Earn        |         ✅        |         —        |          —          |
    | Subaccount management |         ✅        |         —        |          —          |
    | FIX broker allocation |         —        |         —        |    ✅ (Tags 78/79)   |
    | Authentication        |    HMAC-SHA512   | Token (via REST) |   Spot FIX API Key  |
    | Colocation            |         —        |         ✅        |          ✅          |

    <AccordionGroup>
      <Accordion title="REST">
        Best for: operational tasks that don't require real-time streaming — checking balances, querying order history, managing deposits and withdrawals, Earn, sub-account transfers.

        Not recommended for: latency-sensitive order entry or real-time market data. Each request incurs a full HTTP round-trip.

        Base URL: `https://api.kraken.com`
      </Accordion>

      <Accordion title="WebSocket (v2 recommended)">
        Best for: most systematic trading use cases. Real-time order updates, market data streaming, L3 book, and order entry in a single persistent connection. The recommended choice for new integrations.

        Limitations: no Funding or Earn endpoints (use REST for those), no cancel-on-disconnect.

        Endpoint: `wss://ws.kraken.com/v2`
      </Accordion>

      <Accordion title="Unified FIX 4.4">
        Best for: institutional and HFT clients requiring the lowest latency, deterministic message sequencing, cancel-on-disconnect, and session-based message replay. Available for colocated deployments alongside WebSocket.

        Uses a **Spot FIX API Key** pre-configured with the correct permissions. Covers both Spot and Derivatives in a single session.

        Limitations: requires NDA and VIP status for production colocation. Cannot cancel orders from a different FIX session. No account data endpoints.
      </Accordion>
    </AccordionGroup>
  </Tab>

  <Tab title="Derivatives">
    Derivatives has its own trading engine with a separate REST API and WebSocket feed. For lowest-latency order management, use the Unified FIX API.

    |                      |       REST       |        WebSocket       |     Unified FIX     |
    | :------------------- | :--------------: | :--------------------: | :-----------------: |
    | Connection model     | Request/response | Persistent (streaming) |  Persistent session |
    | Latency profile      | Higher, variable |           Low          | Lowest (colocation) |
    | Market data          |         ✅        |            ✅           |          ✅          |
    | Order entry          |         ✅        |            —           |          ✅          |
    | Account data         |         ✅        |            ✅           |          —          |
    | L3 order book        |         —        |            —           |          ✅          |
    | Order amend          |         ✅        |            —           |    ✅ (MsgType=G)    |
    | Cancel on disconnect |         —        |            —           |          ✅          |
    | FIX message replay   |         —        |            —           |          ✅          |
    | Authentication       |    HMAC-SHA512   |         API Key        |   Spot FIX API Key  |
    | Colocation           |         ✅        |            ✅           |          ✅          |

    <Note>
      Derivatives WebSocket is for **streaming market data and account updates only**. Order entry is handled via REST or Unified FIX. Both REST and WebSocket are available for colocated Derivatives deployments.
    </Note>

    <AccordionGroup>
      <Accordion title="Derivatives REST">
        Best for: order management, position queries, account data, funding, and any operation requiring a confirmed response. Available in colocation.

        Base URL: `https://futures.kraken.com/derivatives/api/v3`
      </Accordion>

      <Accordion title="Derivatives WebSocket (streaming only)">
        Best for: real-time market data feeds, account balance updates, and position streaming. Not used for order entry — pair with REST or Unified FIX for order management.

        Endpoint: `wss://futures.kraken.com/ws/v1`

        Available in colocation alongside REST.
      </Accordion>

      <Accordion title="Unified FIX 4.4">
        Best for: lowest-latency order management on Derivatives. Covers both Spot and Derivatives via a single **Spot FIX API Key** — no separate Derivatives FIX credentials required.

        Provides deterministic message sequencing, cancel-on-disconnect, and session-based message replay. Available in colocation.
      </Accordion>
    </AccordionGroup>
  </Tab>

  <Tab title="Spot + Derivatives">
    When trading both markets, each has its own trading engine. The Unified FIX API is the only protocol that covers both markets in a single session.

    | Protocol              | Spot |  Derivatives  | Colocation |
    | :-------------------- | :--: | :-----------: | :--------: |
    | Spot REST             |   ✅  |       —       |      —     |
    | Spot WebSocket        |   ✅  |       —       |      ✅     |
    | Derivatives REST      |   —  |       ✅       |      ✅     |
    | Derivatives WebSocket |   —  | ✅ (streaming) |      ✅     |
    | Unified FIX           |   ✅  |       ✅       |      ✅     |

    **Recommended setup:**

    | Need                               | Protocol                        |
    | :--------------------------------- | :------------------------------ |
    | Spot order entry, low latency      | WebSocket v2 or Unified FIX     |
    | Derivatives order entry            | Unified FIX or Derivatives REST |
    | Spot market data                   | Spot WebSocket v2               |
    | Derivatives market data            | Derivatives WebSocket           |
    | Balances, history, funding         | Spot REST                       |
    | Lowest latency across both markets | Unified FIX (colocation)        |

    <Note>
      Rate limits are separate: Spot limits are shared across Spot REST, WebSocket, and the Spot leg of FIX. Derivatives limits run independently on a per-session basis for FIX and per-account for REST.
    </Note>
  </Tab>
</Tabs>

## Rate limits

| Protocol         | Rate limit scope                                    |
| :--------------- | :-------------------------------------------------- |
| Spot REST        | Account level — shared with Spot WebSocket and FIX  |
| Spot WebSocket   | Account level — shared with Spot REST and FIX       |
| Spot FIX         | Account level — shared with Spot REST and WebSocket |
| Derivatives FIX  | Session level — each FIX session has its own bucket |
| Derivatives REST | Account level — separate from Derivatives FIX       |

<Warning>If you run parallel order management systems across multiple protocols on Spot, they share a single rate counter. A burst on one will affect capacity on the others.</Warning>

## Symbol formats

The same instrument has different identifiers across protocols:

| Instrument                  | REST                    | WebSocket   | FIX (Symbol) |
| :-------------------------- | :---------------------- | :---------- | :----------- |
| Bitcoin / USD               | `XXBTZUSD` or `XBT/USD` | `BTC/USD`   | `XBT/USD`    |
| Ethereum / USD              | `XETHZUSD` or `ETH/USD` | `ETH/USD`   | `ETH/USD`    |
| BTC Perpetual (Derivatives) | `PI_XBTUSD`             | `PI_XBTUSD` | `PI_XBTUSD`  |

<Tip>WebSocket v2 and REST accept the more readable format (e.g. `BTC/USD`). FIX uses the same short format. REST also accepts the legacy Kraken format (e.g. `XXBTZUSD`) for backwards compatibility.</Tip>

## Cancel scope

| Protocol                     | Can cancel orders placed via   |
| :--------------------------- | :----------------------------- |
| REST                         | Any source (REST, WS, FIX, UI) |
| WebSocket                    | Any source (REST, WS, FIX, UI) |
| FIX (single order cancel)    | **Same FIX session only**      |
| FIX (OrderMassCancelRequest) | All orders on the account      |

This is a critical architectural consideration. If your FIX session disconnects and reconnects as a new session, you cannot cancel orders from the previous session using FIX `OrderCancelRequest` — you must use `OrderMassCancelRequest` or fall back to REST/WebSocket.

## Sequencing guarantees

**FIX (sticky routing):** Each FIX session is bound to a specific FIX Gateway instance and follows a deterministic path to the trading engine. New orders and cancels from the same session arrive in order at the engine.

**WebSocket (non-sticky):** Connections are load-balanced. Two messages sent on the same connection may follow different paths and arrive out of order at the engine's inbound queue.

**REST:** No ordering guarantees between separate HTTP requests.

For strategies where the sequence of a cancel and a new order matters (e.g. cancel-replace at a specific price), FIX provides the strongest guarantee.

## WebSocket v1 vs v2

| Feature             | v1            | v2                 |
| :------------------ | :------------ | :----------------- |
| Message format      | Array         | Object             |
| L3 order-by-order   | —             | ✅                  |
| Book checksum       | Updates only  | Snapshot + updates |
| Timestamp precision | Epoch sec, μs | ISO 8601, μs       |
| Trade ID            | —             | Sequential int     |
| New features        | Frozen        | Active development |

v1 is maintained for existing integrations. All new integrations should use v2.

## Related guides

<CardGroup cols={3}>
  <Card title="Quickstart" icon="rocket" href="/home/guides/quickstart">
    Set up your first API key and place your first order
  </Card>

  <Card title="Order lifecycle" icon="arrows-spin" href="/exchange/guides/general/order-lifecycle">
    How order states and transitions work across all protocols
  </Card>

  <Card title="Colocation and connectivity" icon="server" href="/exchange/guides/general/colocation">
    Low-latency connectivity tiers — from cloud to cross-connect
  </Card>

  <Card title="WebSocket reconnection" icon="rotate" href="/exchange/guides/websockets/reconnection">
    Handle disconnects, re-subscription, and state reconciliation
  </Card>

  <Card title="Rate limits" icon="gauge" href="/exchange/guides/general/ratelimits">
    How rate limits work across REST, WebSocket, and FIX
  </Card>

  <Card title="Error reference" icon="triangle-exclamation" href="/exchange/guides/general/errors">
    Full list of error codes and how to handle them
  </Card>
</CardGroup>