What is MEV (maximal extractable value)?

MEV, short for maximal extractable value, is the extra profit someone can make by controlling which transactions go into a block and in what order. On Ethereum, it is value captured beyond the standard block reward and gas fees. The term used to mean miner extractable value, but it changed after Ethereum moved to proof of stake, when validators took over ordering blocks.

How does MEV work on Ethereum?

When you send a transaction on Ethereum, it usually waits in a public pool before going into a block. Anyone can see it there. Specialized players called searchers run algorithms and bots that scan these pending transactions for profitable opportunities. When they find one, they send their own transactions and pay high fees so the block producer orders them in a way that captures the profit. Because the only way to guarantee that ordering is to pay for it, searchers often hand most of their MEV to validators.

Today much of this runs through a system called proposer-builder separation. With MEV-Boost, specialized builders put together whole blocks, relays check them, and validators simply pick the block that pays the most. ethereum.org explains that this setup lets validators outsource block building instead of hunting for MEV themselves.

What are common examples of MEV?

DEX arbitrage is the best known. If a token trades at different prices on two decentralized exchanges, a bot buys on the cheaper one and sells on the other in a single transaction.

Liquidations are another. On lending platforms, loans that fall below required collateral can be liquidated, and whoever does it first earns a fee.

There is also NFT MEV, where the same ordering tricks are used around popular NFT sales.

Not all MEV harms users. ethereum.org notes that arbitrage helps keep prices in line across markets and that liquidations help lending protocols stay solvent.

What is a sandwich attack in crypto?

A sandwich attack is a form of front running aimed at one large trade. A bot spots your pending swap, buys the same token just before you, which pushes the price up, then sells right after your trade goes through. You end up with a worse price, and the bot keeps the difference. This shows up as extra slippage. Some bots, known as generalized front runners, simply copy a profitable pending transaction and resubmit it with a higher fee.

MEV can also hurt the network more broadly. Bidding wars over gas can crowd blocks and raise fees for everyone, and ethereum.org warns that very large MEV could tempt validators to reorganize blocks.

How can you protect yourself from MEV bots?

The main defense is to keep your trade out of the public waiting area. Flashbots Protect is one service that sends Ethereum transactions to a private mempool, hiding them from front running and sandwich bots. According to its docs, it only includes transactions that do not fail, so you are not charged for reverted ones, and it may pay refunds if your transaction creates MEV. As of October 2026, wallets and apps differ in what protections they build in, so check yours.