Order Books versus Automated Market Makers (AMMs)

Two exchanges can show the same token at the same price and still fill your trade in completely different ways. One matches you against a list of other people's orders. The other prices you against a pool of coins and a formula, with no one on the far side at all. Both take your order, both call themselves exchanges, and the difference between them shapes how much your trade moves the price. Knowing which model you are on is worth a minute before you trade.

What is an order book?

An order book is a live list of the buy and sell orders waiting to be filled on a market. Buyers post the prices they are willing to pay (bids) and sellers post the prices they will accept (asks); the exchange's matching engine pairs them whenever a bid meets an ask. The highest bid and the lowest ask sit closest together at the top of the book, and the gap between them is the spread. This is the model most traditional exchanges use, in equities and foreign exchange as well as the larger crypto venues, and it has run in one form or another for centuries.

What is an AMM?

An automated market maker prices trades without an order book, using a pool of two assets and a formula instead of a counterparty. Rather than matching you against another trader, a decentralised exchange holds a pool, say ether and a stablecoin, funded by people called liquidity providers. A formula prices each trade against the current ratio of the two assets in the pool, so you trade with the pool itself. The best-known formula keeps the product of the two balances constant, which is why buying one asset from a pool raises its price for the next buyer. AMMs are what made decentralised exchanges practical, since a formula needs no central matching engine to run.

How do the two price a trade differently?

The order book prices from other people's standing orders; the AMM prices from a formula. On an order book, your trade fills against whatever bids or asks are resting there, so the price you get depends on how deep the queue is at each level. On an AMM, your trade shifts the ratio of assets in the pool, and the formula moves the price along a curve as it goes; the larger your trade relative to the pool, the further along that curve it travels. This built-in movement is called price impact, and it is the AMM's version of what happens on an order book when a large order eats through several price levels. Same effect, different machinery.

Which model has deeper liquidity?

Neither model is deeper by nature; depth depends on the individual market, not the mechanism. A heavily used order-book market on a large token can hold enormous resting size near the top of the book, while a thinly funded pool moves sharply on a modest trade, and the reverse is just as common. What both models share is that liquidity is what decides how gently your trade fills: a deep book or a large pool absorbs your order with little movement, and a thin one on either model walks the price against you. Our note on liquidity (opens in a new tab) covers why that number matters more than the label on the venue.

What does providing AMM liquidity involve?

Providing liquidity to an AMM earns you a share of its trading fees, in exchange for taking on a risk called impermanent loss. When you deposit two assets into a pool, traders swap against them and you collect a cut of each swap's fee. The catch: if the two assets' prices drift apart, the formula rebalances the pool in a way that can leave you worse off than if you had simply held the two assets, and that shortfall is impermanent loss. Fees offset it to some degree, though whether they fully cover it depends on the pool. It is the trade-off at the heart of AMM liquidity, and worth understanding before you supply any.

Where does Northtape fit?

Northtape does not run an order book, host a pool or execute trades. What it does is help you read the market a trade sits in before you make it. Its market view covers the top-100 assets by market cap with 7-day sparklines, and it marks an asset "Tradeable" only when it sits in that top-100 and clears at least US$10M in 24-hour volume.

FAQs

Is a centralised exchange always an order book and a decentralised one always an AMM? Mostly, but not always. Most large centralised exchanges use order books and most decentralised exchanges use AMMs, though some decentralised venues run on-chain order books and the two models increasingly borrow from each other.

Which model is cheaper to trade on? It depends on the market, not the model. Order-book venues usually charge a maker or taker fee, while AMMs take a swap fee that goes to liquidity providers plus network gas on-chain. The bigger cost on either is often price impact on a thin market rather than the headline fee.

What is a liquidity pool? A liquidity pool is the shared reserve of two assets that an AMM prices its trades against. People deposit both assets into it, traders swap against it, and the depositors earn a share of the fees.

Why does a large trade move the price more on an AMM? Because an AMM prices along a formula tied to the pool's balances, every unit you buy shifts the ratio and raises the price for the next unit. A larger trade travels further along that curve, so it moves the price more than a small one against the same pool.

None of this is investment advice. How a trade fills depends on live liquidity that changes second by second on both models, so treat any description here as how the mechanism works rather than a guide to a particular trade, and check the spread or price impact your own interface shows before you confirm.