What is MEV, and who is taking it?

A swap settles at a worse price than the screen quoted, and nothing about the transaction looks broken. It was signed, broadcast and included in a block. In between, software read it while it waited, worked out what it would do to the pool, and landed two of its own transactions either side of it. No rule was broken. The order transactions settle in is worth money, and that is the whole subject.

What is MEV?

Maximal extractable value (MEV) is the profit available to whoever decides the order of transactions inside a block. It comes from choosing what goes in, what order it settles in and what is left out, not from holding an asset or predicting a price. The term entered use as miner extractable value in Flash Boys 2.0, a 2019 paper by Philip Daian and seven co-authors; the first word changed once Ethereum moved to proof of stake and miners no longer ordered anything.

A blockchain has no fair queue and never promised one. Transactions wait in a public pool before inclusion, and whoever builds the next block chooses from that pool. Nothing in the protocol requires first-come, first-served, so a builder is free to sort by whatever pays most.

Who extracts it?

Three roles share the work: searchers, builders, and the validator proposing the block. A searcher runs software that watches pending transactions for a profitable pattern, and submits a bundle of its own. A builder assembles whole blocks from those bundles. Ordinary traffic then competes on what the finished block is worth. The proposer picks the most valuable block on offer and signs it.

Most Ethereum blocks now come from that outside market rather than from the validator proposing them, through software known as MEV-Boost. Relay data published through September 2026 indicates that a small number of builders assemble the majority of blocks between them. That concentration raises the same question as validator centralisation (opens in a new tab): a market with few participants can be pressured in ways that a crowded market cannot.

What does it look like on a real trade?

Three patterns cover most of it: arbitrage, liquidation and sandwiching. Arbitrage closes a price gap between two venues inside a single block, and it is the least contested form since it pushes two prices together. Liquidation extraction is the bonus a lending protocol pays whoever closes a position that has fallen below its required collateral, which is why a liquidation (opens in a new tab) is usually taken within a block, or more of becoming available.

Sandwiching is the pattern that costs an ordinary trader directly. A searcher spots a large pending swap against an automated market maker (AMM), buys the same asset just ahead of it, lets the swap fill at the price that buy has pushed up, then sells straight after. What the trader sees afterwards is slippage (opens in a new tab) they cannot tell apart from ordinary market movement, since the fill price is the only evidence they get.

Why can't a chain order transactions fairly?

No fair order exists to enforce. Nodes receive transactions at different moments and in different sequences, so "the order they arrived in" is not a single fact anyone can point at. Something has to settle the tie, and the tie-breaker every chain reaches for is the fee attached. That turns position inside a block into an auction, which is what a gas (opens in a new tab) bidding contest is underneath.

Visibility is the other half. A transaction sitting in a public pool tells anyone watching what it will do, at what size and against which pool, seconds before it is final. Extraction depends on that preview more than on any smart contracts.

What limits it?

Four things can reduce it, but none of them stops it completely. A tight slippage limit caps what a sandwich can take, since a trade that would fill outside the limit reverts instead. Sending a transaction through a private channel to a builder keeps it out of the public pool, though that moves the trust from an open queue to one company. Batch settlement removes the advantage of being first inside an interval: the venue clears every trade in it at one price.

The fourth is changing how the blockchain itself works. Proposer-builder separation splits the two jobs so a validator need not run extraction software to earn what its block is worth, which addresses the centralisation risk more than the extraction itself. Nothing makes ordering worthless, and a chain where ordering carries value will have someone competing to do it.

Where Northtape fits

Northtape proposes no blocks, runs no validators and routes no trades. It is a news desk. Stories about MEV exploits and validator behaviour are detected by the Risk Radar protocol lens.

FAQs

Does MEV only exist on Ethereum? No. Any chain whose blocks are assembled by someone choosing an order has the same opening, which includes most Layer 2 networks (opens in a new tab), where a single sequencer often sets the order on its own.

Is sandwiching illegal? It is not prohibited by the chain, which is the only rulebook the transaction itself touches. Whether it breaches a securities or market-conduct law depends on the jurisdiction and the venue, and no settled answer covers every market.

Can I see it happening to my own trade? Only after the fact. A block explorer (opens in a new tab) shows the transactions sharing a block with yours, so a buy from one address just before your swap and a sell from the same address just after is the shape to recognise.

Does paying a higher fee protect me? No. Paying more improves your place in the queue, though a searcher can pay more again, and a builder is under no obligation to sort by fee at all.

None of this is investment advice. It describes how blocks are assembled, not whether to trade on-chain, where or at what size. Transaction ordering can work against a trade in ways a fill price alone does not reveal, and nothing here suggests where any price may go next.