MEV (Maximal Extractable Value)
Maximal extractable value, or MEV, is the extra profit that can be made by deciding which transactions go into a block and in what order. Specialized bots and block producers capture it through arbitrage, liquidations and, more controversially, by trading around ordinary users.
Where MEV comes from
On public blockchains such as Ethereum, pending transactions usually wait in a public mempool before they are included in a block. Anyone can see them. Whoever builds the block decides the order, and order matters: a large trade on a decentralized exchange moves the price, and someone who trades just before or after it can profit.
The term originally stood for miner extractable value. After Ethereum moved to proof of stake in 2022, it was renamed maximal extractable value, since validators rather than miners now propose blocks.
Who extracts it
Today, most MEV on Ethereum is found by searchers, automated bots that scan the mempool for opportunities and bundle transactions. They pass these bundles to block builders, who assemble profitable blocks and bid for the right to have validators propose them. Much of the profit ends up as payments to validators.
Common strategies include arbitrage between exchanges, triggering liquidations on lending protocols for a reward, and sandwich attacks on users' swaps.
Good MEV and bad MEV
Some MEV performs a useful job. Arbitrage keeps prices aligned across exchanges, and liquidation bots keep lending protocols solvent. Other forms extract value directly from users. Say you submit a swap with a 3% slippage tolerance. A bot can buy right before you and sell right after, leaving you with a worse price and pocketing the difference.
MEV can also push up gas fees as bots compete, and it encourages concentration among a few large builders, which raises concerns about censorship.
How users reduce exposure
Setting a tight slippage limit, splitting large trades and using services that send transactions privately to block builders rather than to the public mempool can reduce the risk. None of these remove MEV entirely, because it is a structural feature of public, ordered transaction processing.
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Frequently asked questions
Is MEV illegal?
MEV extraction happens through the open rules of the blockchain and its legal status is largely untested. Specific schemes, such as exploiting bugs to manipulate blocks, have led to criminal charges, so the answer depends on the method.
Does MEV exist on blockchains other than Ethereum?
Yes. Any blockchain where block producers can order transactions and where on-chain trading happens has MEV, including Solana and many layer 2 networks, though its form differs.
How do I know if I lost money to MEV?
Block explorers and specialised tools can show whether your swap was surrounded by bot transactions in the same block. A noticeably worse execution price than quoted is one hint.
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