Liquidity Pools and AMMs: How DeFi Swaps Work Without the Jargon

A liquidity pool is a smart contract that holds reserves of two or more tokens so people can trade against the pool instead of waiting for a matching buyer or seller, and an automated market maker is the formula that decides the price of each trade. Once you separate those two ideas, most of DeFi swapping stops feeling like magic.

If you have ever opened a decentralized exchange, seen a price appear instantly, and wondered who exactly you were buying from, you are asking the right question. There is no person on the other side. You are trading against a pool of tokens, and a formula is setting the price. At Blockready, we teach this mechanism-first, because the single biggest source of DeFi confusion is treating "liquidity pool" and "automated market maker" as the same thing. They are not. One is the inventory. The other is the pricing rule. Keep those apart and the rest falls into place.

This article explains how that works in plain language, where the price actually comes from, why someone would put their tokens into a pool, and which risks belong to traders versus the people supplying the liquidity. It is a companion to the broader picture of how DeFi works without banks, narrowed down to the one mechanism that powers most on-chain trading.

What a liquidity pool actually is

Start with the definition, because the words get blurred constantly.

An automated market maker (AMM) is a different thing. It is the rule that prices a trade against the pool. According to Uniswap's developer documentation, a swap takes tokens from one side of the pool and adds tokens to the other, and the AMM formula calculates how much you receive based on the pool's current balances. So the pool answers "where do the tokens come from?" and the AMM answers "how is the price calculated without an order book?"

A decentralized exchange, or DEX, is the venue you actually click on. Many DEXs use AMMs, but the two are not identical. A DEX is the storefront, the AMM is the cash register logic, and the pool is the stock on the shelves.

You trade against a pool, not a person

Traditional exchanges run on order books. Buyers post bids, sellers post asks, and a trade happens when two orders meet. That model works well on centralized platforms, and if you want the full picture of order books and centralized exchanges, that mechanism is worth understanding on its own. The problem is that running a live order book directly on a blockchain is slow and expensive, because every order, update, and cancellation can become its own on-chain transaction.

AMMs sidestep that. Instead of matching you with a counterparty, they let you trade against pooled inventory using a formula. The Bank for International Settlements, in its review of automated market making in DeFi, describes this as replacing the order book with liquidity providers who fund a pool and a mathematical rule that prices trades against it. You do not need to find a willing seller. You need a pool deep enough to fill your trade at a price you accept.

That shift is the heart of DeFi trading, and it is also where beginners get stuck, because four separate things are happening at once and most explainers blur them together. Here is the model we use to keep them straight.

Where the price actually comes from

The most common AMM is a constant-product pool. It tries to keep the product of its two token reserves constant after every trade, written as x * y = k. Here, x is the amount of one token in the pool, y is the amount of the other, and k is the number that should not fall after a trade.

When you buy a token out of the pool, that token leaves and the token you paid with enters. Because the product has to stay balanced, the price shifts: the token you are buying becomes scarcer inside the pool, so each additional unit costs more. That is why a large trade relative to the pool's size gets a worse average price. It is not a hidden fee. It is the curve doing its job. Here is the sequence in practice.

One question follows naturally: if the pool only knows its own balances, how does its price ever track the wider market? The answer is arbitrage. If a pool prices ETH below other markets, traders buy the cheap ETH from the pool and sell it elsewhere, which pushes the pool's price back in line. Arbitrage is not a glitch. It is the mechanism that keeps AMM prices useful, and it quietly matters for liquidity providers, as you will see in a moment.

It also helps to keep two terms separate, because they often get used interchangeably. Price impact is the price change your own trade causes by shifting the pool's balances. Slippage is the gap between the price you were quoted and the price you actually got, often because the pool state changed between your quote and your transaction confirming. Pool depth affects both: a deeper pool moves less, a shallow pool moves a lot.

Two users, two risk stories

This is the part most guides flatten into one generic "risks" list. Swapping and providing liquidity are different activities with different risks, and confusing them leads to real mistakes.

On the trader side, the sharpest edge is usually MEV. Bots watch pending transactions and can place orders around yours to profit from the price movement you are about to cause, a pattern Ethereum's own documentation describes under maximal extractable value. Setting a sensible slippage limit and avoiding oversized trades into shallow pools both help.

On the liquidity provider side, the headline risk is impermanent loss, the gap between holding two tokens in a pool and simply holding them in your wallet when their prices move apart. It is the direct consequence of that arbitrage process: as the pool rebalances, it tends to hold more of whatever is falling and less of whatever is rising. We keep the full worked example in our dedicated guide to impermanent loss, so here it is enough to know it exists and that swap fees are meant to offset it, not guarantee a profit.

That last point is where a lot of beginners get hurt. Supplying liquidity is often sold as passive income, but fee income is compensation for taking risk, not free yield. If you want to understand where DeFi yield actually comes from, the honest version is that an LP's outcome depends on fees earned, token price movement, impermanent loss, any bonus incentives, and gas costs, all netted together. Some pools reward their providers well. Others quietly lose money for them. The mechanism does not promise either outcome.

Liquidity is not legitimacy

One misconception is worth flagging on its own, because it costs people money.

Seeing a token sitting in a pool with a clean price chart feels reassuring. It should not. The liquidity tells you the plumbing works, not that the project behind the token is sound. Project evaluation is a separate skill, and it belongs to careful research, not to the presence of a pool.

Not all pools work the same way

The 50/50 constant-product pool is the best starting model, but modern DeFi runs on several pool designs, and assuming they are all the same is its own trap. A few worth recognizing, kept deliberately brief:

Stable-swap pools are built for assets meant to stay close in value, such as two stablecoins. The Curve StableSwap design uses a curve that keeps slippage low while prices stay near each other. It reduces normal slippage for correlated assets, but it does not remove the risk that a stablecoin depegs.

Weighted pools do not have to be 50/50. As Balancer's weighted pool documentation explains, a pool can hold more than two tokens or use ratios like 80/20, behaving a little like a self-rebalancing basket. Different weights change the exposure and the loss profile, so they are not automatically safer.

Concentrated liquidity lets providers place their liquidity in a chosen price range rather than across all prices. This can make capital far more efficient, but it turns liquidity provision into an active job, because a position can drift out of range and stop earning.

Hook-enabled pools are the newest layer. Uniswap v4, live since January 2025, introduced hooks, which are modular pieces of code that let developers customize how a pool handles swaps, fees, and LP positions, as described in the official Uniswap v4 announcement. The practical takeaway for a beginner is simple: "AMM" is no longer one fixed design, so it is worth checking what kind of pool you are actually using.

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