__NOTICE__: This document is a work-in-progress for researchers and implementers. This is an accompanying document to [Ethereum 2.0 Phase 0 -- Honest Validator](0_beacon-chain-validator.md) that describes an API exposed by the beacon node, which enables the validator client to participate in the Ethereum 2.0 protocol.
## Outline
This document outlines a minimal application programming interface (API) which is exposed by a `BeaconNode` for use by a `ValidatorClient` which aims to facilitate [_phase 0_](../../README.md#phase-0) of Ethereum 2.0.
The beacon node maintains the state of the beacon chain by communicating with other beacon nodes in the Ethereum Serenity network. Conceptually, it does not maintain keypairs that participate with the beacon chain.
The validator client is a conceptually separate entity which utilises private keys to perform validator related tasks on the beacon chain, which we call validator "duties". These duties includes the production of beacon blocks and signing of attestations.
The goal of this specification is to promote interoperability between beacon nodes and validator clients derived from different projects. For example, the validator client from Lighthouse, could communicate with a running instance of the beacon node from Prysm.
This specification is derived from a proposal and discussion on Issues [#1011](https://github.com/ethereum/eth2.0-specs/issues/1011) and [#1012](https://github.com/ethereum/eth2.0-specs/issues/1012)
The API specification has been written in [OpenAPI 3.0](https://swagger.io/docs/specification/about/) and is provided in the [beacon_node_oapi.yaml](beacon_node_oapi.yaml) file alongside this document.