Order Book

An order book on a cryptocurrency exchange is a real-time, continuously updated list of all outstanding buy and sell orders for a specific trading pair, organized by price. Buy orders, known as bids, represent the prices and quantities at which traders are willing to purchase the asset. Sell orders, known as asks or offers, represent the prices at which sellers are willing to part with their holdings. The difference between the highest bid and the lowest ask is called the spread, which is one of the key measures of market liquidity.

Order books provide a transparent window into supply and demand dynamics at any given moment. Large clusters of orders at specific price levels, known as walls, can act as support or resistance levels — a large buy wall below the current price may slow a downward move, while a large sell wall above may cap upward momentum. Traders use order book analysis to gauge market sentiment, identify potential price turning points, and estimate how large their own orders can be before causing significant price impact.

For algorithmic traders, the order book is a critical data source. Many automated strategies rely on real-time order book data to make trading decisions, from simple strategies that trigger orders when the spread narrows to sophisticated market-making bots that continuously post and adjust orders on both sides of the book. Exchanges provide API access to order book data, allowing trading bots to consume this information at high speed. Understanding the structure and dynamics of the order book is one of the most important skills for anyone designing or evaluating algorithmic trading strategies.