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

The builder has been verified as of this commit bf3d41f026e9728233dd3e1c40e75c49b9ae00b3. 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

Once installed, we are ready to run the builder.

Syncing nodes

Before we can run the builder, we need to sync a CL and EL node pair on our target network.

The remainder of this document will assume we are building for the sepolia network.

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

The builder requires a synced CL client like Lighthouse. You can find instructions on how to sync a lighthouse node here.

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

Doing the initial/bulk sync from the mev builder should be possible, but has not been tested.

The recommended approach will be to run reth (ideally built from source at the same commit pinned in this repo) for the target network alongside the CL until the pair has reached the head of the chain.

Example commands utilizing checkpoint sync following the Lighthouse book to do this:

  1. Make the JWT secret (refer to the Lighthouse guide for more info).

  2. [recommended] Obtain a checkpoint sync URL if you wish to use this sync mode.

  3. Run reth:

reth --chain sepolia \
  node \
  --http \
  --authrpc.jwtsecret $JWT_SECRET_FILE_PATH
  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

The pair should start syncing. Once the pair of nodes is fully synced you can stop reth and run the mev builder in its place.

You should be able to skip this step Syncing nodes and just proceed directly to running the CL and mev builder in the next step, as the builder should also sync if needed. But note:

  1. running the builder without having a synced database already has not been tested
  2. the builder will wait anyway until the head of the chain has been synced

Run the builder on a synced chain

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.

To configure the builder, 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.
  • jwt_secret_path: ensure this value matches the one used previously when doing the initial sync.

Once the configuration looks good, you can run the builder as follows alongside lighthouse.

lighthouse has some additional configuration from above to ensure the builder always receives head updates from the chain.

  1. Run mev with config file config.toml:
mev --network sepolia build config.toml
  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

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 --network sepolia build config.toml