Builder Quickstart

External builders can submit blocks to the Flashbots Relays on Mainnet, Goerli and Sepolia networks.

Getting Started

1. Read the documentation — Familiarize yourself with the Flashbots Block Builders Official Documentation.

2. Understand the API — Review the Relay API documentation - Block Builder API.

3. Join the community — Participate in the Block Builder Self-Help Group forum for support and discussion.

4. Reference implementation — Check out boost-geth-builder, an example builder implementation built by Flashbots.

How Block Building Works

1. Builders construct full blocks by ordering transactions to maximize MEV extraction and validator rewards.
2. Builders submit blocks to one or more relays via the Builder API.
3. Relays validate the blocks and make them available to proposers via MEV-Boost.
4. Proposers (validators running MEV-Boost) select the most profitable block header.
5. The relay reveals the full block contents once the proposer signs the header.

Builder API

Builders interact with relays using the Builder API specification. Key endpoints include:

• POST /relay/v1/builder/blocks — Submit a new block
• GET /relay/v1/builder/validators — Get the list of registered validators

Resources

• Flashbots Builder Docs
• Builder API Specs
• Block Builder Self-Help Group
• boost-geth-builder (reference implementation)