MEV for Traders: What It Costs You and What Helps

Maximal extractable value is the profit available to whoever decides the order of transactions in a block. Some of it is benign — arbitrage between venues keeps prices consistent and is a service. Some of it is taken directly from the traders whose transactions are being reordered, and that portion is a cost worth understanding because it is partly controllable.

The sandwich, precisely

You submit a swap. Before it executes it sits in a public queue where anyone can read it, including your declared maximum acceptable price.

An observer places a buy immediately before yours, pushing the price up. Your trade then executes against the worse price, pushing it up further. They sell immediately after, into the price your own trade created. Their profit is your worse fill, and everything about it is ordinary, valid, on-chain activity.

The mechanism has one property that matters more than the rest: the profit available is bounded by your slippage tolerance. That setting is a declaration of how much worse a price you will accept, and it is read by the people deciding whether the attack is worth performing.

Why the standard advice makes it worse

When a transaction reverts for slippage, every interface and every guide suggests raising the tolerance. It works, in the sense that the transaction then succeeds.

It also widens the window. A trade with a generous tolerance is a more attractive target than the same trade with a tight one, because the extractable amount is larger. The user has responded to a failed transaction by making the next one more expensive, and nothing in the interface tells them so.

The correct response to repeated reverts is usually smaller orders, a deeper pool, or private routing — not a wider tolerance. A tight tolerance that occasionally fails is cheaper over time than a wide one that always succeeds.

Defences that work

Private transaction routing sends the transaction directly to block builders rather than to the public queue, so it is not visible to observers before inclusion. This eliminates the class rather than mitigating it, and it is available through several wallets as an ordinary setting. The trade is a dependency on the relay you route through.

Tight slippage tolerance bounds the extractable amount directly. Set it as low as the market allows and accept occasional failure.

Smaller orders reduce the price movement your trade creates, and the profit available scales with that movement. Splitting a large trade helps for this reason as well as for price impact.

Deeper pools mean less movement for the same size, so venue selection is itself a defence.

Batch and intent-based venues change the model entirely: rather than broadcasting an order, you express a desired outcome and solvers compete to fill it, with settlement at a uniform price for the batch. That removes the ordering advantage that makes the attack possible.

What the defences do not cover

Private routing hides the transaction from the public queue and not from the builder receiving it. That relocates the trust rather than removing it, and the relevant question becomes the builder's policy rather than the queue's visibility.

Nothing addresses arbitrage that follows your trade legitimately. If your order moves a price out of line with other venues, someone will correct it and profit. That is the market functioning, and the cost is your price impact rather than an extraction from you.

Working out what you are paying

• Compare your realised price against the pool price immediately before your transaction. Consistent adverse difference is the signal.
• Check whether your losses scale with your slippage setting. If they do, it is ordering rather than market movement.
• Try the same trade through a private route and compare outcomes across several attempts.
• Watch whether the pool price returns to roughly its prior level immediately after your trade — that reversion is the shape of a sandwich.
• For anything large enough to matter, use private routing by default rather than as a response to having been hit.

The uncomfortable summary is that transacting in public has a price, it is not disclosed anywhere, and the wallet setting most people adjust to fix a different problem is the one that sets it.