How Does the Execution of a Limit Order Differ on a CEX versus a DEX?

On a CEX, a limit order is placed on a central, off-chain order book and is matched by the exchange's private matching engine according to price-time priority. Execution is instant and guaranteed if the price is met.

On a DEX, a limit order is often executed by a decentralized relay or a third-party filler bot. The order is a signed message that becomes a transaction only when the market price meets the limit price, and the filler bot executes it on-chain.

Execution is not guaranteed due to network congestion or MEV.