This repository provides a basic builder which can submit blocks to mev-boost relays using the Relay APIs.

The builder is built as an extension to the reth execution layer (EL) client and also requires a consensus layer (CL) client to run.

The default builder simply uses reth's local mempool when sourcing transactions.


Build from source

The best way to run the builder right now is to build this project from source.


Follow the steps here under Dependencies.

Build mev-rs

You can install the mev-rs binary, named mev, with the following steps:

git clone
cd mev-rs
cargo install --locked --path bin/mev

The builder has been verified as of this commit 08973a298268a3ad5f5d2c247b69b47dbb7bf97f. No guarantees about other states of the repository currently.

The cargo install command should place the mev binary under the default .cargo/bin folder which is also in your PATH following the suggested Rust installation process.

Run the builder


To run the mev builder, first you should make the appropriate configuration. You can make a local copy of example.config.toml to get started.

First, you will need to construct a JWT secret for use in the Engine API. You can refer to these instructions from the Lighthouse guide to see how to do this.

Ensure the network key in the TOML matches the target network you wish to run the builder on. This network applies to any of the mev-rs tools that consume this configuration. The remainder of this document (including examples below) will assume we are building for the sepolia network.

To configure the builder specifically, you can edit the fields under the [builder] key of the TOML.

Fields you should change:

  • execution_mnemonic: update to a seed phrase of an ethereum wallet you control. This wallet will be used to author payment transactions to the proposer and also is used as the source of funds for any subsidy value you wish to add to the block. You can select a particular index (following BIP-39) by terminating the seed phrase with a :N and integer index N. Otherwise the builder will just use the first index from the key tree.
  • subsidy_gwei: set this value to 0 if your execution layer address has no ETH in it; otherwise, the blocks will be invalid.


Once the configuration looks good, you can run the builder as follows alongside lighthouse. If you are running from a fresh install or have fallen far enough behind the tip of the chain, the CL and EL nodes will sync. To expedite syncing times, use of checkpoint sync is recommended. You can see more info in this guide from the Lighthouse book.

Repository has only been tested on the Sepolia network and there is no guarantee the builder works on other networks.

Repository has only been tested with Lighthouse and there is no guarantee other CLs will work.

  1. Run mev with config file config.toml:
mev build node --mev-builder-config config.toml --authrpc.jwtsecret $JWT_SECRET_FILE_PATH

NOTE: mev build exposes the same CLI interface as stock reth, so refer to that command's help for further settings you may be interested in.

  1. Run lighthouse:
lighthouse --network sepolia \
  bn \
  --http \
  --execution-endpoint http://localhost:8551 \
  --execution-jwt $JWT_SECRET_FILE_PATH \
  --disable-deposit-contract-sync \
  --checkpoint-sync-url $CHECKPOINT_SYNC_PROVIDER
  --suggested-fee-recipient $FEE_RECIPIENT

NOTE: the builder will not be active until the local CL and EL are fully synced.

Additional notes

  • The --suggested-fee-recipient for lighthouse is ultimately not used, but currently required to run the node. Any valid address should do and it should not affect the builder.
  • If you are seeing slow or lagging operation, you can try to adjust the preparation lookahead with the --prepare-payload-lookahead option on lighthouse.
  • The builder has been tested on an AWS EC2 instance of t3.xlarge variety with a 512Gb disk.
  • You can control the logging level of reth and mev with the RUST_LOG environment variable. For example, to silence the reth logs, you can run mev like RUST_LOG=mev=info mev build config.toml