DEX (Decentralised Exchange) is a crypto trading venue where users swap tokens directly from their own wallets through smart contracts, with no operator taking custody of funds or matching orders. Settlement happens in the same on-chain transaction as the trade, so there is no withdrawal queue and no exchange balance to lose if an operator fails. Most DEXs use automated market makers: liquidity providers deposit token pairs into pools, prices follow the reserve ratio, and each swap pays a fee to those providers. Price impact grows with trade size relative to pool depth. Users pay network fees, face front-running bots and carry contract-bug risk. MiCA excludes only fully decentralised services, which few DEXs are in practice.
How does a DEX work
Most DEXs use an automated market maker (AMM) rather than an order book. Liquidity providers deposit two tokens into a pool, and the contract quotes prices from the ratio of the reserves. On Uniswap v2 the rule is x × y = k: the product of the two reserve balances must not fall after a trade. Each swap pays a 0.30% fee, which is added to the reserves and earned by liquidity providers when they withdraw their share.
Because the price only changes when someone trades, a DEX price can drift away from prices elsewhere. Arbitrageurs then buy on the cheaper venue and sell on the dearer one until the gap closes, which is the mechanism that keeps AMM prices close to the wider market.
DEX price impact: a worked example
Take an illustrative pool holding 100 ETH and 300,000 USDC, implying a price of 3,000 USDC per ETH. A trader swapping 3,000 USDC receives about 0.987 ETH, an effective price of roughly 3,039, about 1.3% above the starting price once the fee and impact are counted. A trader swapping 30,000 USDC receives about 9.07 ETH, an effective price near 3,309, more than 10% worse. The deeper the pool relative to trade size, the lower the impact, which is why liquidity depth is the main quality measure for a DEX.
DEX vs CEX
A centralised exchange holds client assets, runs KYC, matches orders off-chain and can offer fiat on- and off-ramps. A DEX holds nothing on behalf of users and usually has no onboarding, but users pay network fees on every trade, face front-running by bots that see pending transactions, and carry the risk of contract bugs. Large trades tend to be cheaper on a CEX with a deep order book; long-tail tokens are often only available on DEXs.
Is a DEX regulated
Recital 22 of MiCA, Regulation (EU) 2023/1114, places crypto-asset services provided in a fully decentralised manner without any intermediary outside the regulation. Few DEXs are fully decentralised in practice: a company may run the website, hold an upgrade key or collect an interface fee. Gibraltar's Financial Services Commission lists DEX operators among the business models it assesses case by case under its DLT provider framework, and FinCEN's 2019 guidance applies money transmitter rules to the owners or operators of a decentralised application that transmits value.
For a buyer of a licensed exchange or broker, routing client orders to DEXs raises questions diligence has to answer: who holds the keys that sign those trades, how best execution and sanctions screening are evidenced, and whether the CASP authorisation covers execution on third-party venues.