> ## 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 > > **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. Periodic full L2 orderbook snapshots for a single market. On subscribe, the server sends the current book up to `nLevels` price levels per side, then continues to broadcast a fresh full snapshot every ~500ms. No incremental updates — each message replaces the prior book state. Use `l2OrderbookUpdates` if you need to maintain your own local book. ## AsyncAPI ````yaml api-reference/asyncapi.yaml l2Orderbook id: l2Orderbook title: L2 orderbook 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. Periodic full L2 orderbook snapshots for a single market. On subscribe, the server sends the current book up to `nLevels` price levels per side, then continues to broadcast a fresh full snapshot every ~500ms. No incremental updates — each message replaces the prior book state. Use `l2OrderbookUpdates` if you need to maintain your own local book. 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=l2Orderbook parameters: [] bindings: [] operations: - &ref_2 id: subscribeL2Orderbook title: Subscribe l2 orderbook type: receive messages: - &ref_4 id: subscribe contentType: application/json payload: - name: Subscribe to L2 Orderbook type: object properties: - name: type type: string description: subscribe required: true - name: channel type: string enumValues: - l2Orderbook - 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 snapshot. Range 1–100. required: false headers: [] jsonPayloadSchema: type: object required: - type - channel - id properties: type: type: string const: subscribe x-parser-schema-id: channel: type: string enum: - l2Orderbook - 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 snapshot. Range 1–100. default: 20 minimum: 1 maximum: 100 x-parser-schema-id: x-parser-schema-id: SubscribeL2OrderbookPayload title: Subscribe to L2 Orderbook example: |- { "type": "subscribe", "channel": "l2Orderbook", "id": "BTC-USD", "nLevels": 50 } bindings: [] extensions: - id: x-parser-unique-object-id value: subscribe bindings: [] extensions: &ref_1 - id: x-parser-unique-object-id value: l2Orderbook - &ref_3 id: receiveL2Orderbook title: Receive l2 orderbook type: send messages: - &ref_5 id: snapshot contentType: application/json payload: - allOf: &ref_0 - 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 bindings: [] extensions: *ref_1 sendOperations: - *ref_2 receiveOperations: - *ref_3 sendMessages: - *ref_4 receiveMessages: - *ref_5 extensions: - id: x-parser-unique-object-id value: l2Orderbook securitySchemes: [] ````