> ## Documentation Index > Fetch the complete documentation index at: https://docs.arcus.xyz/llms.txt > Use this file to discover all available pages before exploring further. # L2 orderbook updates > > **Endpoint:** `wss://api.testnet.arcus.xyz/v1/ws` — one socket multiplexes every channel and RPC request. Click **Connect**, then send the example subscribe message below to start receiving data. Full L2 orderbook snapshot followed by event-driven incremental deltas for a single market. On subscribe: full snapshot up to `nLevels` per side, then delta updates as orders are placed, modified, or cancelled. Each delta carries a monotonically increasing `lastSequenceId` (continuous with the snapshot's `lastSequenceId`) — drop or re-subscribe on any gap. ## AsyncAPI ````yaml api-reference/asyncapi.yaml l2OrderbookUpdates id: l2OrderbookUpdates title: L2 orderbook updates description: > > **Endpoint:** `wss://api.testnet.arcus.xyz/v1/ws` — one socket multiplexes every channel and RPC request. Click **Connect**, then send the example subscribe message below to start receiving data. Full L2 orderbook snapshot followed by event-driven incremental deltas for a single market. On subscribe: full snapshot up to `nLevels` per side, then delta updates as orders are placed, modified, or cancelled. Each delta carries a monotonically increasing `lastSequenceId` (continuous with the snapshot's `lastSequenceId`) — drop or re-subscribe on any gap. servers: - id: testnet protocol: wss host: api.testnet.arcus.xyz bindings: [] variables: [] - id: mainnet protocol: wss host: api.arcus.xyz bindings: [] variables: [] address: /v1/ws?channel=l2OrderbookUpdates parameters: [] bindings: [] operations: - &ref_4 id: subscribeL2OrderbookUpdates title: Subscribe l2 orderbook updates type: receive messages: - &ref_6 id: subscribe contentType: application/json payload: - name: Subscribe to L2 Orderbook incremental updates type: object properties: - name: type type: string description: subscribe required: true - name: channel type: string description: l2OrderbookUpdates required: true - name: id type: string description: Market display name (e.g. "BTC-USD", "ETH-USD"). required: true - name: nLevels type: integer description: Price levels per side in the initial snapshot. Range 1–100. required: false - name: snapshot type: boolean description: >- When false, suppress the initial book snapshot on subscribe and stream only incremental delta updates. Defaults to true. required: false headers: [] jsonPayloadSchema: type: object required: - type - channel - id properties: type: type: string const: subscribe x-parser-schema-id: channel: type: string const: l2OrderbookUpdates x-parser-schema-id: id: type: string description: Market display name (e.g. "BTC-USD", "ETH-USD"). example: BTC-USD x-parser-schema-id: nLevels: type: integer description: Price levels per side in the initial snapshot. Range 1–100. default: 20 minimum: 1 maximum: 100 x-parser-schema-id: snapshot: type: boolean description: >- When false, suppress the initial book snapshot on subscribe and stream only incremental delta updates. Defaults to true. default: true x-parser-schema-id: x-parser-schema-id: SubscribeL2OrderbookUpdatesPayload title: Subscribe to L2 Orderbook incremental updates example: |- { "type": "subscribe", "channel": "l2OrderbookUpdates", "id": "BTC-USD", "nLevels": 50 } bindings: [] extensions: - id: x-parser-unique-object-id value: subscribe bindings: [] extensions: &ref_3 - id: x-parser-unique-object-id value: l2OrderbookUpdates - &ref_5 id: receiveL2OrderbookUpdates title: Receive l2 orderbook updates type: send messages: - &ref_7 id: snapshot contentType: application/json payload: - allOf: &ref_0 - &ref_1 type: object description: Common envelope for all server-pushed channel messages. required: - type - channel properties: type: type: string enum: - subscribed - channel_data description: >- `subscribed` for the initial snapshot; `channel_data` for updates. x-parser-schema-id: channel: type: string description: Channel name. x-parser-schema-id: id: type: string description: >- Channel id (market or address). Absent for global channels. x-parser-schema-id: contents: type: object additionalProperties: true description: Channel-specific payload. Schema varies by channel. properties: {} x-parser-schema-id: x-parser-schema-id: ChannelDataEnvelope - type: object properties: type: const: subscribed x-parser-schema-id: contents: type: object required: - bids - asks - lastSequenceId properties: bids: type: array description: >- Price levels, best bid first. Each entry is `[price, size]`. items: type: array minItems: 2 maxItems: 2 items: type: string x-parser-schema-id: x-parser-schema-id: example: - - '94500.0' - '1.5' - - '94499.0' - '2.0' x-parser-schema-id: asks: type: array description: >- Price levels, best ask first. Each entry is `[price, size]`. items: type: array minItems: 2 maxItems: 2 items: type: string x-parser-schema-id: x-parser-schema-id: example: - - '94501.0' - '0.8' - - '94502.0' - '3.1' x-parser-schema-id: lastSequenceId: type: integer description: >- Per-market orderbook sequence of the last update reflected in this snapshot. Reconcile `l2OrderbookUpdates` deltas against this — apply deltas whose `lastSequenceId` exceeds it. example: 1042 x-parser-schema-id: globalSequenceId: type: integer description: Cross-market monotonic sequence. Omitted when zero. example: 880421 x-parser-schema-id: timestamp: type: integer format: int64 description: >- Unix microseconds when the snapshot was taken. Omitted when zero. example: 1780410803123456 x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: L2OrderbookSnapshotPayload name: L2 Orderbook Snapshot headers: [] jsonPayloadSchema: allOf: *ref_0 x-parser-schema-id: L2OrderbookSnapshotPayload title: L2 Orderbook Snapshot example: |- { "type": "subscribed", "channel": "l2Orderbook", "id": "BTC-USD", "contents": { "bids": [ [ "94500.0", "1.5" ], [ "94499.0", "2.0" ] ], "asks": [ [ "94501.0", "0.8" ], [ "94502.0", "3.1" ] ], "lastSequenceId": 1042, "globalSequenceId": 880421, "timestamp": 1780410803123456 } } bindings: [] extensions: - id: x-parser-unique-object-id value: snapshot - &ref_8 id: update contentType: application/json payload: - allOf: &ref_2 - *ref_1 - type: object properties: type: const: channel_data x-parser-schema-id: contents: type: object description: > Incremental delta. Each `[price, size]` entry sets that level's absolute size; `size: "0"` means the level was removed. Drop or re-subscribe on any `lastSequenceId` gap. required: - bids - asks - lastSequenceId - globalSequenceId properties: bids: type: array items: type: array minItems: 2 maxItems: 2 items: type: string x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: asks: type: array items: type: array minItems: 2 maxItems: 2 items: type: string x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: lastSequenceId: type: integer description: >- Per-market orderbook sequence for this delta. Monotonically increasing and continuous with the snapshot's `lastSequenceId`. x-parser-schema-id: globalSequenceId: type: integer description: Cross-market monotonic sequence. x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: x-parser-schema-id: L2OrderbookUpdatePayload name: L2 Orderbook Incremental Update description: > `size: "0"` means the level was removed. Drop or re-subscribe on any `lastSequenceId` gap. headers: [] jsonPayloadSchema: allOf: *ref_2 x-parser-schema-id: L2OrderbookUpdatePayload title: L2 Orderbook Incremental Update description: > `size: "0"` means the level was removed. Drop or re-subscribe on any `lastSequenceId` gap. example: |- { "type": "channel_data", "channel": "l2OrderbookUpdates", "id": "BTC-USD", "contents": { "bids": [ [ "94499.0", "0" ] ], "asks": [ [ "94503.0", "1.2" ] ], "lastSequenceId": 1043, "globalSequenceId": 880422 } } bindings: [] extensions: - id: x-parser-unique-object-id value: update bindings: [] extensions: *ref_3 sendOperations: - *ref_4 receiveOperations: - *ref_5 sendMessages: - *ref_6 receiveMessages: - *ref_7 - *ref_8 extensions: - id: x-parser-unique-object-id value: l2OrderbookUpdates securitySchemes: [] ````