> ## Documentation Index > Fetch the complete documentation index at: https://docs.decibel.trade/llms.txt > Use this file to discover all available pages before exploring further. # Market depth > Order book depth for one Decibel market address, perp or spot, with aggregated price levels. Spot BTC and perp BTC are different markets with different addresses and require separate subscriptions. The depth payload does not carry `asset_type`; the subscribed market address identifies the product. Optional aggregationLevel parameter (1, 2, 5, 10, 100, or 1000) can be appended to the topic and defaults to 1. Spot clients derive mid price from `best_bid` and `best_ask` because spot markets do not publish `market_price`. ## AsyncAPI ````yaml api-reference/asyncapi.json marketDepth id: marketDepth title: Market depth description: >- Order book depth for one Decibel market address, perp or spot, with aggregated price levels. Spot BTC and perp BTC are different markets with different addresses and require separate subscriptions. The depth payload does not carry `asset_type`; the subscribed market address identifies the product. Optional aggregationLevel parameter (1, 2, 5, 10, 100, or 1000) can be appended to the topic and defaults to 1. Spot clients derive mid price from `best_bid` and `best_ask` because spot markets do not publish `market_price`. servers: - id: testnet protocol: wss host: api.testnet.aptoslabs.com/decibel/ws bindings: [] variables: [] address: depth:{marketAddr}:{aggregationLevel} parameters: - id: aggregationLevel jsonSchema: type: string description: Price aggregation level for order book depth (1, 2, 5, 10, 100, or 1000) description: Price aggregation level for order book depth (1, 2, 5, 10, 100, or 1000) type: string required: true deprecated: false - id: marketAddr jsonSchema: type: string description: Market address (Aptos address format, e.g. 0x456...) description: Market address (Aptos address format, e.g. 0x456...) type: string required: true deprecated: false bindings: [] operations: - &ref_3 id: receivemarketDepth title: Receivemarket depth description: >- Receive updates for order book depth for one decibel market address, perp or spot, with aggregated price levels. spot btc and perp btc are different markets with different addresses and require separate subscriptions. the depth payload does not carry `asset_type`; the subscribed market address identifies the product. optional aggregationlevel parameter (1, 2, 5, 10, 100, or 1000) can be appended to the topic and defaults to 1. spot clients derive mid price from `best_bid` and `best_ask` because spot markets do not publish `market_price`. type: receive messages: - &ref_4 id: MarketDepthMessage payload: - name: MarketDepthMessage description: >- Order book depth for one Decibel market address, perp or spot, with aggregated price levels. Spot BTC and perp BTC are different markets with different addresses and require separate subscriptions. The depth payload does not carry `asset_type`; the subscribed market address identifies the product. Optional aggregationLevel parameter (1, 2, 5, 10, 100, or 1000) can be appended to the topic and defaults to 1. Spot clients derive mid price from `best_bid` and `best_ask` because spot markets do not publish `market_price`. type: object properties: - name: asks type: array required: true properties: - name: price type: number required: true - name: size type: number required: true - name: best_ask type: &ref_0 - number - 'null' description: >- True best ask price (pre-aggregation), useful for accurate spread calculation at higher aggregation levels required: false - name: best_bid type: &ref_1 - number - 'null' description: >- True best bid price (pre-aggregation), useful for accurate spread calculation at higher aggregation levels required: false - name: bids type: array required: true properties: - name: price type: number required: true - name: size type: number required: true - name: market type: string required: true - name: topic type: string required: true - name: unix_ms type: integer description: Latest transaction timestamp in milliseconds required: true headers: [] jsonPayloadSchema: type: object required: - topic - market - bids - asks - unix_ms properties: asks: type: array items: &ref_2 type: object required: - price - size properties: price: type: number format: double x-parser-schema-id: size: type: number format: double x-parser-schema-id: x-parser-schema-id: NormalizedPriceLevel x-parser-schema-id: best_ask: type: *ref_0 format: double description: >- True best ask price (pre-aggregation), useful for accurate spread calculation at higher aggregation levels x-parser-schema-id: best_bid: type: *ref_1 format: double description: >- True best bid price (pre-aggregation), useful for accurate spread calculation at higher aggregation levels x-parser-schema-id: bids: type: array items: *ref_2 x-parser-schema-id: market: type: string x-parser-schema-id: topic: type: string x-parser-schema-id: unix_ms: type: integer format: int64 description: Latest transaction timestamp in milliseconds x-parser-schema-id: x-parser-schema-id: MarketDepthResponse title: Market depth message description: >- Order book depth for one Decibel market address, perp or spot, with aggregated price levels. Spot BTC and perp BTC are different markets with different addresses and require separate subscriptions. The depth payload does not carry `asset_type`; the subscribed market address identifies the product. Optional aggregationLevel parameter (1, 2, 5, 10, 100, or 1000) can be appended to the topic and defaults to 1. Spot clients derive mid price from `best_bid` and `best_ask` because spot markets do not publish `market_price`. example: |- { "topic": "depth:0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890:1", "market": "0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890", "bids": [ { "price": 50000, "size": 10.5 }, { "price": 49950, "size": 15.2 }, { "price": 49900, "size": 20 } ], "asks": [ { "price": 50050, "size": 8.3 }, { "price": 50100, "size": 12.7 }, { "price": 50150, "size": 18.5 } ], "unix_ms": 1699564800000, "best_bid": 50000, "best_ask": 50050 } bindings: [] extensions: - id: x-parser-unique-object-id value: MarketDepthMessage - id: x-parser-message-name value: MarketDepthMessage bindings: [] extensions: - id: x-parser-unique-object-id value: marketDepth sendOperations: - *ref_3 receiveOperations: [] sendMessages: - *ref_4 receiveMessages: [] extensions: - id: x-parser-unique-object-id value: marketDepth securitySchemes: [] ````