The Ethereum Builder API Specification offers a comprehensive interface for consensus layer clients to leverage externally constructed blocks, crucial for effective staking pool operation. As a temporary yet pivotal solution pending proposer-builder separation (PBS) on the Beacon chain, the Builder API enables block proposers to utilize a “blind” execution layer header. By doing so, it balances trust assumptions without altering the base protocol, operating on a “MEV-Boost” architecture. This approach allows proposers to be bound to a builder’s blind header, ensuring integrity and preventing transaction tampering through an innovative signing protocol. The repository accommodates API specifications across forks, builder software, and contributing guidelines, with seamless integration facilitated by builder multiplexers like mev-boost and mev-rs. Additionally, local spec rendering and release processes, including API specification linting and version updates, are streamlined to foster collaborative development and continuous integration.