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+# Relay specs
+
+## Table of contents
+<!-- TOC -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+- [Introduction](#introduction)
+- [Notation](#notation)
+- [Custom types](#custom-types)
+- [Constants](#constants)
+- [Containers](#containers)
+  - [`​GET /relay​/v1​/builder​/validators` response type](#%E2%80%8Bget-relay%E2%80%8Bv1%E2%80%8Bbuilder%E2%80%8Bvalidators-response-type)
+    - [`ProposerDutiesResponse`](#proposerdutiesresponse)
+    - [`BuilderGetValidatorsResponseEntry`](#buildergetvalidatorsresponseentry)
+    - [`SignedValidatorRegistration`](#signedvalidatorregistration)
+    - [`RegisterValidatorRequestMessage`](#registervalidatorrequestmessage)
+  - [`​POST /relay​/v1​/builder​/blocks` request type](#%E2%80%8Bpost-relay%E2%80%8Bv1%E2%80%8Bbuilder%E2%80%8Bblocks-request-type)
+    - [`BuilderSubmitNewBlockRequest`](#buildersubmitnewblockrequest)
+    - [`SubmitBlockRequest`](#submitblockrequest)
+    - [`BidTrace`](#bidtrace)
+    - [`ExecutionPayload`](#executionpayload)
+    - [`Withdrawal`](#withdrawal)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+## Introduction
+
+This document presents the `mev-boost` relay specification. 
+
+[`mev-boost`](https://boost.flashbots.net/) is an out-of-protocol mechanism to
+connect Ethereum Proof-of-Stake validators to the external block-building market.
+The [validator-side](https://github.com/flashbots/mev-boost) API is specified 
+in the [builder specs](https://github.com/ethereum/builder-specs). The [relay-side](https://github.com/flashbots/mev-boost-relay) API is specified here in the relay specs. 
+
+## Notation
+
+Code snippets appearing in `this style` are to be interpreted as Python 3 code.
+
+## Custom types
+
+We define the following Python custom types for type hinting and readability:
+
+| Name | SSZ equivalent | Description |
+| - | - | - |
+| `Slot` | `uint64` | a slot number |
+| `ValidatorIndex` | `uint64` | a validator registry index |
+| `Gwei` | `uint64` | an amount in Gwei |
+| `Hash32` | `Bytes32` | a 256-bit hash |
+| `BLSPubkey` | `Bytes48` | a BLS12-381 public key |
+| `BLSSignature` | `Bytes96` | a BLS12-381 signature |
+| `ExecutionAddress` | `Bytes20` | Address of account on the execution layer |
+| `Transaction` | `ByteList[MAX_BYTES_PER_TRANSACTION]` | either a [typed transaction envelope](https://eips.ethereum.org/EIPS/eip-2718#opaque-byte-array-rather-than-an-rlp-array) or a legacy transaction|
+| `WithdrawalIndex` | `uint64` | an index of a `Withdrawal` |
+<!-- |`Gwei`|  -->
+
+## Constants
+
+The following values are (non-configurable) constants used throughout the specification.
+
+
+| Name | Value |
+| - | - |
+| `BYTES_PER_LOGS_BLOOM` | `uint64(2**8)` (= 256) |
+| `MAX_EXTRA_DATA_BYTES` | `2**5` (= 32) |
+| `MAX_BYTES_PER_TRANSACTION` | `uint64(2**30)` (= 1,073,741,824) |
+| `MAX_TRANSACTIONS_PER_PAYLOAD` | `uint64(2**20)` (= 1,048,576) |
+| `MAX_WITHDRAWALS_PER_PAYLOAD` | `uint64(2**4)` (= 16) |
+
+
+## Containers
+
+*Note*: Fields missing in container instantiations default to their zero value.
+
+### `​GET /relay​/v1​/builder​/validators` response type 
+
+#### `ProposerDutiesResponse`
+
+```python
+class ProposerDutiesResponse(Container):
+    data: List[BuilderGetValidatorsResponseEntry]
+```
+
+#### `BuilderGetValidatorsResponseEntry`
+
+```python
+class BuilderGetValidatorsResponseEntry(Container):
+    slot: Slot
+    validator_index: ValidatorIndex
+    entry: SignedValidatorRegistration
+```
+
+#### `SignedValidatorRegistration`
+
+```python
+class SignedValidatorRegistration(Container):
+    message: RegisterValidatorRequestMessage
+    signature: BLSSignature
+```
+
+#### `RegisterValidatorRequestMessage`
+
+```python
+class RegisterValidatorRequestMessage(Container):
+    fee_recipient: ExecutionAddress
+    gas_limit: uint64
+    timestamp: uint64
+    pubkey: BLSPubkey
+```
+
+### `​POST /relay​/v1​/builder​/blocks` request type 
+
+#### `BuilderSubmitNewBlockRequest`
+
+```python
+class BuilderSubmitNewBlockRequest(Container):
+    capella: SubmitBlockRequest
+```
+
+#### `SubmitBlockRequest`
+
+```python
+class SubmitBlockRequest(Container):
+    message: BidTrace
+    execution_payload: ExecutionPayload 
+    signature: BLSSignature
+```
+
+#### `BidTrace`
+
+```python
+class BidTrace(Container):
+    slot: Slot
+    parent_hash: Hash32
+    block_hash: Hash32
+    builder_pubkey: BLSPubkey
+    proposer_pubkey: BLSPubkey
+    proposer_fee_recipient: ExecutionAddress
+    gas_limit: uint64
+    gas_used: uint64
+    value: uint256
+```
+
+#### `ExecutionPayload` 
+
+From [capella spec](https://github.com/ethereum/consensus-specs/blob/f7352d18cfb91c58b1addb4ea509aedd6e32165c/specs/capella/beacon-chain.md#executionpayload).
+
+```python
+class ExecutionPayload(Container):
+    parent_hash: Hash32
+    fee_recipient: ExecutionAddress
+    state_root: Bytes32
+    receipts_root: Bytes32
+    logs_bloom: ByteVector[BYTES_PER_LOGS_BLOOM]
+    prev_randao: Bytes32
+    block_number: uint64
+    gas_limit: uint64
+    gas_used: uint64
+    timestamp: uint64
+    extra_data: ByteList[MAX_EXTRA_DATA_BYTES]
+    base_fee_per_gas: uint256
+    block_hash: Hash32 
+    transactions: List[Transaction, MAX_TRANSACTIONS_PER_PAYLOAD]
+    withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD] 
+```
+
+#### `Withdrawal`
+
+From [capella spec](https://github.com/ethereum/consensus-specs/blob/f7352d18cfb91c58b1addb4ea509aedd6e32165c/specs/capella/beacon-chain.md#withdrawal).
+
+```python
+class Withdrawal(Container):
+    index: WithdrawalIndex
+    validator_index: ValidatorIndex
+    address: ExecutionAddress
+    amount: Gwei
+```
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