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

# OrderBookIncremental

> Market data schema, template 2

<div className="api-banner">
  <span className="api-protocol ws">SBE</span>
  <span className="api-detail">schema 34 · market data</span>
  <span className="api-tag">template 2</span>
</div>

Order-by-order (L3) book updates for one instrument.

**Direction:** Kraken → client

| ID | Field | Type | Encoding | Presence | Description |
| :- | :- | :- | :- | :- | :- |
| 1 | `instrumentId` | [`InstrumentId`](/exchange/api-reference/sbe/market-data-types#instrumentid) | field | required | |
| 2 | `orderBookSeq` | `uint64` | field | required | Contiguous per-instrument update sequence, starting at one |
| 3 | `transactTime` | [`TimestampNs`](/exchange/api-reference/sbe/market-data-types#timestampns) | field | required | Time the matching event occurred at the source |
| 4 | `orders` | group | group | required | |
| 1 |   ↳ `updateAction` | [`OrderUpdateAction`](/exchange/api-reference/sbe/market-data-types#orderupdateaction) | group field | required | |
| 2 |   ↳ `side` | [`Side`](/exchange/api-reference/sbe/market-data-types#side) | group field | required | |
| 3 |   ↳ `orderId` | [`OrderId`](/exchange/api-reference/sbe/market-data-types#orderid) | group field | required | |
| 4 |   ↳ `price` | [`Price`](/exchange/api-reference/sbe/market-data-types#price) | group field | required | |
| 5 |   ↳ `quantity` | [`Quantity`](/exchange/api-reference/sbe/market-data-types#quantity) | group field | required | |
| 6 |   ↳ `orderPriority` | `uint64` | group field | required | Opaque queue priority comparable within one price level |

Rows marked ↳ are fields of the repeating group above them. Each group is preceded by a `groupSizeEncoding` header (`blockLength`, `numInGroup`).

Every message is preceded by the standard SBE `messageHeader` (`blockLength`, `templateId`, `schemaId`, `version`). See [encodings](/exchange/api-reference/sbe/market-data-types#messageheader).