CEX vs DEX: how centralized and decentralized crypto exchanges differ

What is the basic difference between a CEX and a DEX?#

Both are places to swap one asset for another. A Federal Reserve note sums up the difference: “at a high level, DEXs seek to perform a similar function for users”, but they differ in several critical ways ^[1]. The most important difference for a beginner is custody — who controls the coins while you trade.

On a centralized exchange (CEX), ethereum.org explains, “you have to deposit your assets before the trade and trust them to look after them” ^[2]. On a decentralized exchange (DEX), a type of app that lets you swap tokens with peers on the network ^[3], the trade is executed by a smart contract and the tokens return straight to your wallet. Uniswap, a DEX protocol built on Ethereum, describes its protocol as designed for “self-custody” ^[4]. For the wallet side of this choice, read custodial vs self-custody.

Generalised from the Federal Reserve note, ethereum.org and Uniswap documentation cited on this page. Individual platforms vary.

How do prices work on each type of exchange?#

A CEX keeps an order book: a list of bids and asks from traders and market makers, matched by the exchange’s engine. The Federal Reserve note says CEXs “operate using traditional market makers and limit order books”, while DEXs “use automated market makers” ^[1].

An automated market maker (AMM) replaces the order book with a pool of two tokens. Uniswap prices trades with the constant product formula x × y = k, where x and y are the pool’s reserves; the formula means “larger trades relative to pool depth move the price more” ^[4]. Each Uniswap v2 trade pays a 0.3% fee that goes to the pool’s liquidity providers ^[5]. Arbitrage traders keep the pool’s price close to the wider market, because they trade whenever the pool price is wrong by more than the fee ^[6].

Each trade: input after fee = amount × 0.997; new USDC reserve = 200,000 + input; new ETH reserve = k ÷ new USDC reserve; ETH out = 100 − new ETH reserve. The lesson matches the order-book case: the bigger your trade relative to the pool, the worse your average price.

What does a DEX swap involve, step by step?#

A token swap on a DEX

The approval step deserves care. Revoke.cash explains that token approvals give a smart contract permission to spend your tokens on your behalf, and that DEXs commonly need them ^[7]. Approving a malicious contract can let it drain that token later — see token approvals and wallet drainers.

What are the risks of using a centralized exchange?#

When an exchange holds your coins, its problems become your problems. Ethereum.org warns that if the exchange “has financial trouble, your funds would be at risk” ^[8], and that deposited assets are exposed because centralized exchanges “are attractive targets for hackers” ^[2]. The SEC’s investor alert adds that crypto platforms may combine exchange, broker and custody functions that regulated markets keep separate, which “creates conflicts of interest and risks for investors” ^[9].

• No deposit insurance. The SEC notes that bank-style FDIC insurance and SIPC broker protections do not cover accounts with crypto asset entities ^[9].
• Withdrawal halts and bankruptcy. Some crypto firms have suspended withdrawals or entered bankruptcy, and customers “might not be able to get those assets back when they want to” ^[9].
• Proof of reserves is limited. The SEC warns such reports may be only a snapshot and “may not provide any meaningful assurance” that customer balances are fully backed ^[9].

What are the risks of using a decentralized exchange?#

Keeping custody removes the exchange-failure risk but hands you every other job. Uniswap stresses that its core contracts are non-upgradeable and that no party can “pause them, reverse trade execution, or change protocol behavior retroactively” ^[4]. That also means nobody can reverse your mistake. Specific risks include:

• Fake tokens and pools. Anyone can create a pool for any token, so look-alike tokens can appear. Check the contract address from an official source.
• Front-running. On public blockchains, bots can see pending trades. Ethereum.org explains that “sandwich” attacks leave users facing “increased slippage and worse execution” ^[10].
• Thin pools. As the example above shows, a large swap in a small pool can cost several percent in price impact.
• Smart-contract and interface risk. A bug in a contract, or a fake website imitating a real DEX, can lose funds with no one to call.

How did CEXs and DEXs behave under stress?#

The Federal Reserve studied trading during the March 2023 stablecoin turmoil. It found that DEX volumes jumped to more than $20 billion on March 11, compared with typical volumes of $1 billion to $3 billion, while CEX volumes rose far less dramatically ^[1]. Its authors concluded that the two types of venue “operate differently during times of crisis, though they price stablecoins very similarly” ^[1]. In short: prices stayed closely aligned, but where people chose to trade shifted.

How are CEXs and DEXs regulated?#

Rules differ by country, and this is not legal advice. In the European Union, the MiCA regulation lists operating a trading platform, exchanging crypto-assets for funds and providing custody among the services a crypto-asset service provider performs ^[11]. It also states that where services are provided “in a fully decentralised manner without any intermediary”, they should not fall within its scope ^[11]. Whether a given DEX qualifies as fully decentralised is a legal question. In the US, the SEC’s 2023 investor alert warned that none of the major crypto asset entities is registered with it as a broker-dealer, exchange or investment adviser ^[9].

What mistakes do beginners make here?#

• Leaving everything on an exchange

  Coins held by a CEX are a claim on that company. If it fails or halts withdrawals, you may wait a long time or recover little.

• Approving unlimited spending without thinking

  A DEX approval can outlive the trade. Review and revoke approvals you no longer need.

• Ignoring price impact on small pools

  The quoted price is for a tiny trade. Check the output amount and the price impact for your full size.

• Trusting a link to a “DEX”

  Fake front-ends imitate real ones. Type the address yourself or use a bookmark you created.

Frequently asked questions#

The bottom line#

A CEX asks you to trust a company with your coins in exchange for convenience, bank connections and an order book. A DEX lets you keep your coins but makes you responsible for every approval, address and click.

If you are just starting, learn how decentralized exchanges work and how order books price your trade before you move real money on either.

Sources#