The order book is the core matching mechanism on a crypto exchange. Every buy or sell order submitted by a user is sent into that book, where buyers meet sellers and pending orders wait to be matched. It updates in real time, so both price levels and available size can change from moment to moment.
Three parts make up the order book display
In the CEX.IO Trade page described in the source material, the order book contains buy orders, sell orders, and trade history. Buy orders list bids, showing the price and quantity a trader wants to purchase. Sell orders list asks, showing the asking price and the amount offered for sale. Trade history, shown at the bottom of the Trade page, records transactions that have already been completed in the book.
On the interface, the order book sits below the Market Depth chart and is split into two tables: Buy Orders and Sell Orders. Together, they show how unfilled interest is distributed across price levels.
Why the top of the book matters
Buy orders are ranked in descending order, which puts the highest bid at the top of the buy side. Sell orders are ranked in ascending order, so the lowest ask sits at the top of the sell side. A trade is executed when the highest bid matches the lowest ask, and transactions continue at that same price until the available size on one side is exhausted.
That rule has a direct trading implication. If a trader places a buy order that is not lower than the current cheapest sell order, that order gets filled first. The same applies on the other side: if a sell order is placed at a price no higher than the current top bid, it becomes first in line for execution.
What traders look for in order book imbalance
Order books can also hint at short-term pressure between pending buyers and sellers. The source notes that if the number and size of buy orders are meaningfully larger than sell orders, that may suggest buying pressure that could push price upward in the near term. Heavy concentrations of sell orders can show the opposite side of the market more clearly.
Traders also use the book to spot possible support and resistance levels. A large cluster of buy orders around one price may be treated as support, while a large block of sell orders near another level may be viewed as resistance. Even so, these readings only describe current order placement and do not guarantee a price reaction.
Real-time changes limit how far order book signals can go
The source makes one caution very clear: order books are dynamic at all times. Orders at each price level can be changed, removed, or filled at any moment. Because of that, making trading decisions based only on a single snapshot of the order book may not be a good idea.
For crypto traders, the order book is useful for reading market structure, execution priority, and short-term supply and demand clues. It is still only one tool on the trading screen. The original material also includes a risk notice stating that the content is for information purposes only, not investment or financial advice, and that digital assets involve risk.