How to read an order book
Buy orders, the bids, are listed from the highest price down, and sell orders, the asks, from the lowest price up. The gap between the top of each side is the spread, and the quantity at each level is the depth.
Orders at the same price queue by arrival time. A new order that crosses the spread trades at once against the top of the other side, and any other limit order joins its queue.
The book changes many times a second. Exchanges publish it as a snapshot followed by a stream of updates, with aggregated levels for most users and order-by-order data for professional ones.
What MiCA says about publishing the order book
In the EU, Article 76 of MiCA requires a trading platform to publish its bid and ask prices and the depth at those prices continuously during trading hours. The information is offered on a reasonable commercial basis, made available free of charge 15 minutes after publication in a machine-readable format, and kept published for at least two years.
Why the order book matters to an exchange
The book is what a trader sees first: a tight spread and deep levels signal that orders will fill at fair prices. An empty book signals the opposite, which is why new venues arrange liquidity before opening.
Not every trading product has one. An on-ramp, a broker app or an OTC desk shows a single quoted price, and a decentralised exchange may price from a liquidity pool.
Order book, matching engine or trade history?
- Matching engine
- The software that keeps the book and pairs orders into trades. The order book is the data it works on.
- Trade history
- The list of trades already done. The order book holds only the orders still open.
Where an order book shows up in a platform
Modules that do the work
- Matching engineA low-latency order book for spot markets, with market makers and outside liquidity.
- Market dataLive and historical prices for crypto, stocks and FX, from the data vendors you choose.
Platforms that need it
Guides that go deeper
Where it is written
The laws and standards this page's facts come from.
General information, not legal advice: what applies to you depends on your services and your market.