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.

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	—	✅	✅

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

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

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.

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	✅	✅	✅

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.

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

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.

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.

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)

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.

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

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.

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

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.

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

Quickstart

Set up your first API key and place your first order

Order lifecycle

How order states and transitions work across all protocols

Colocation and connectivity

Low-latency connectivity tiers — from cloud to cross-connect

WebSocket reconnection

Handle disconnects, re-subscription, and state reconciliation

Rate limits

How rate limits work across REST, WebSocket, and FIX

Error reference

Full list of error codes and how to handle them