Order Book

Anatomy of an order book

The standard structure:

• Bids — buy orders ranked by price (highest first).
• Asks — sell orders ranked by price (lowest first).
• Bid-ask spread — gap between best bid and best ask.
• Depth — quantity available at each price level.

A liquid market has many orders at small price increments; illiquid markets have wide gaps.

How orders interact

When a new order arrives:

• Market order — matches immediately against existing orders at best available prices.
• Limit order — only fills at specified price or better; otherwise sits in book.
• Crossing orders — when bid meets ask, trade executes.
• Walking the book — large orders consume multiple price levels.

Matching engines process this in microseconds for liquid markets.

What order books reveal

A few patterns:

• Liquidity — total quantity available across price levels.
• Imbalance — more buying than selling pressure or vice versa.
• Hidden orders — some orders are "iceberg" type (visible quantity smaller than total).
• Pattern interpretation — trading-pattern recognition by sophisticated traders.

Order book reading is a core skill for active traders.

CEX order books

Most centralized exchanges run order-book matching:

• Stock exchanges (NYSE, NASDAQ) — order books central to operation.
• Crypto CEXes (Binance, Coinbase, Kraken) — same model.
• Commercial reach — some exchanges show full order book; others only top levels.

These produce the spreads and liquidity most traders see daily.

DEX order books vs. AMMs

A key distinction:

• DEX order books — Hyperliquid, dYdX, some others. Traditional matching on-chain or in optimized off-chain layer.
• AMMs — Uniswap, Curve, others. Algorithmic pricing based on pool reserves rather than discrete orders.

Each has trade-offs:

• Order books — better for liquid pairs; tighter spreads with deep liquidity.
• AMMs — better for less-liquid pairs; capital-efficient for stable pools.

Most major DEXes have started with AMMs. Newer DEXes have built sophisticated on-chain order books.

High-frequency trading and order books

A specialized world:

• Sophisticated firms continuously add and cancel orders.
• Co-location — physical proximity to exchange matching engines for sub-millisecond latency.
• Specialized infrastructure — networking, computing optimized for speed.
• Market making — provide liquidity for spread capture.

HFT contributes to tighter spreads on liquid markets but raises questions about market structure.

Iceberg orders and hidden liquidity

Not all orders are visible:

• Iceberg orders — large orders that show only a small visible portion.
• Hidden orders — completely invisible until executed.
• Dark pools — separate venues with no order-book transparency.

These reduce information leakage for large orders but obscure market state.

Order types

Beyond basic market and limit:

• Stop orders — trigger when price reaches threshold.
• Stop-limit — combine stop and limit.
• Trailing stops — move with price.
• Fill-or-kill — must fill entirely or not at all.
• Immediate-or-cancel — fill what's available; cancel rest.
• Good-til-cancelled — stay active until manually cancelled.

Different order types serve different use cases.

Crypto order books

A few characteristics specific to crypto:

• 24/7 trading — no market close.
• Wide variation in liquidity across exchanges and pairs.
• Cross-exchange arbitrage keeps prices roughly aligned but with persistent small differences.
• High-frequency activity by sophisticated bots.

For active crypto traders, choosing exchanges with deep order books for the specific pair is important.

What individuals should know

For most traders:

• Liquid major pairs have reliable order books with tight spreads.
• Less-liquid markets have wide spreads and shallow depth.
• Use limit orders for any non-trivial size in less-liquid markets.
• Understand depth before placing large orders.

For sophisticated participants:

• Order book analysis can inform short-term trading decisions.
• Hidden liquidity complicates simple pattern reading.
• Different exchanges have different microstructures.

The order book is the fundamental mechanism through which most non-AMM trading happens. Understanding its dynamics is foundational to active trading and provides context for why prices move as they do even for passive holders.