MEV-Boost is open-source middleware that lets Ethereum validators obtain execution blocks from an external builder market. Developed by Flashbots, it implements proposer-builder separation outside Ethereum’s core consensus rules. A validator can use it to compare bids relayed from builders instead of relying only on a locally assembled execution payload.
Builders, relays, and proposers
Builders assemble transaction payloads and submit bids through relays. A relay checks submitted blocks and exposes a bid with a blinded payload header. The proposer commits by signing the blinded block; the relay then supplies the payload needed for publication. MEV-Boost can connect to multiple relays, aggregating their bids for the consensus client. Builder, relay, and validator are distinct roles even when an organization operates more than one.
What the validator receives
A builder’s bid offers value to the block proposer. The amount varies with transaction demand, available order flow, competition, and the particular slot. It is not a fixed staking bonus. When comparing revenue, avoid counting the same execution fees both inside the builder payment and again as a separate guaranteed income stream. Consensus rewards are governed by Ethereum’s own rules.
Trust and availability
Relays occupy a trusted position between builders and proposers. Their validity checks, availability, timing, and handling of payloads matter. Connecting to several relays can broaden access but does not prove the builder market is decentralized or eliminate censorship concerns. Client-specific fallback and circuit-breaker behavior also matters when an external payload is unavailable.
MEV-Boost versus transaction protection
A validator’s block-sourcing tool is different from a wallet’s private transaction-routing service. Running MEV-Boost does not by itself promise that every transaction is protected from sandwiching. It also does not increase Ethereum’s base transaction capacity. Its purpose is to connect proposers to an external block-building market.
Related Terms
See Also
- What Is MEV — And Why Every Ethereum Transaction Is a Game
- Is Ethereum Staking Making the Network More Centralized?
- Does Ethereum TPS Include Layer 2 Transactions?
Sources
- Flashbots — MEV-Boost Overview — Explains the middleware, the builder market, and integration with consensus clients.
- Flashbots — Relay Fundamentals — Describes relay trust, payload exchange, and client-specific circuit-breaker behavior.
- Flashbots MEV-Boost repository — Official source code and operational documentation for relay-connected block sourcing.
- Ethereum.org — Maximal Extractable Value — Explains the broader MEV market and proposer/builder trade-offs.