mev-boost is open source middleware run by validators to access a competitive block-building market. MEV-Boost was built by Flashbots as an implementation of proposer-builder separation (PBS) for proof-of-stake (PoS) Ethereum.

With MEV-Boost, validators can access blocks from a marketplace of builders. Builders produce blocks containing transaction orderflow and a fee for the block proposing validator. Separating the role of proposers from block builders promotes greater competition, decentralization, and censorship-resistance for Ethereum.