Engine API: A Visual Guide - HackMD

The Engine API coordinates block validation and block proposal between an Ethereum node's execution and consensus layers, and this guide walks through its main flows and failure cases. It is based on the Shanghai spec and assumes the validator builds blocks locally. The guide covers node startup, where the consensus client calls engine_exchangeCapabilities and engine_forkchoiceUpdatedV2, and block building, where engine_getPayloadV2 retrieves a payload from a build process started by a prior forkchoice update. It also describes how block validation via engine_newPayloadV2 can return VALID, INVALID or SYNCING, with error codes such as -38003 for invalid payload attributes and -32602 for wrong payload attributes version.