What is MEV-Boost?

Software that lets an Ethereum validator outsource block building to a competitive market of builders and take the highest bid, rather than assembling a block itself.

It runs alongside a validator's normal client software and is optional, but widely adopted, because a validator that builds its own blocks earns less than one that sells the right to build. Most Ethereum staking operations, from large services down to solo stakers, run it.

The thing it is often confused with is maximal extractable value itself. MEV-Boost does not create MEV. It is the plumbing that routes MEV revenue from specialist builders to ordinary stakers, and in doing so it decides who gets to order transactions.

How it works

The design separates the role of proposing a block from the role of building one, an arrangement usually described as proposer-builder separation.

1. Searchers scan pending transactions and assemble profitable bundles, such as an arbitrage between two decentralized exchanges.
2. Builders collect bundles and ordinary transactions and construct a full block, bidding a payment to the proposer for the right to have it included.
3. Relays sit between builders and proposers. They hold the block contents, verify validity, and pass only the header and the bid to the validator.
4. The validator signs the header committing to the highest bid, before ever seeing the contents. Only then does the relay release the full block.

That last step is the security property. Because the proposer commits blind, it cannot read the block, steal the profitable bundle, and build its own version instead.

The cost is concentration. Building competitively requires specialist infrastructure, so a small number of builders produce most blocks, and relays become chokepoints that can filter transactions. A role the protocol intended to be spread across thousands of validators is in practice performed by a handful of firms.

Example

Illustrative flow. A searcher spots a $900 arbitrage opportunity created by a large pending swap. It builds a bundle that captures it and offers most of the profit to a builder. The builder includes the bundle in a block and bids $700 to the proposer.

A second builder, without that bundle, can only bid $80 from ordinary priority fees. The validator running MEV-Boost signs the $700 header without seeing either block. The staker earns $700 on top of the normal issuance for that slot, and the searcher and builder split the remainder.

Why it matters when you buy

If you stake through an exchange, part of the yield quoted to you originates here, which is one reason published staking rates vary between providers offering the same asset. The rates and terms each venue publishes are collected on the yield pages. If you swap on a decentralized exchange, the other side of the same system is why your fill can be worse than quoted, and a private transaction route is the usual mitigation.

Related terms

• mev — the value this system routes
• validator — the party being paid
• block proposer — the role split from building
• front running — one source of the profit
• sandwich attack — the retail-facing cost
• staking — where the revenue ends up

Questions

Does MEV-Boost make my swaps worse?

Not by itself. It creates an efficient market for block space that rewards searchers, and some of those searchers profit from sandwiching retail swaps. Private transaction routing and a tight slippage tolerance are the practical defenses.

Do I need to know about this to stake through an exchange?

No, but it explains why quoted rates differ between providers for the same asset. Part of a staking yield comes from block building revenue, not just protocol issuance.

Is this part of Ethereum itself?

No. It is separate software with its own relays and builders. Proposals to bring some of this arrangement into the protocol have been discussed for years but are not in place.