Skip to main content

API Reference

BuilderNet provides these APIs:

eth_sendBundle​

You can use eth_sendBundle to send a bundle of transactions to BuilderNet. You can also use eth_sendBundle to replace - or cancel - a previously sent bundle.

What is a bundle

A bundle is a list of signed transactions that are executed atomically. If any transaction in the bundle fails, the entire bundle fails. This is useful for sending multiple transactions that depend on each other.

Request ​

{
    "id": 1,
    "jsonrpc": "2.0",
    "method": "eth_sendBundle",
    "params": [{
        txs               // Array[String], A list of signed transactions to execute in an atomic bundle
        blockNumber       // String, a hex encoded block number for which this bundle is valid on
        minTimestamp      // (Optional) Number, the minimum timestamp for which this bundle is valid, in seconds since the unix epoch
        maxTimestamp      // (Optional) Number, the maximum timestamp for which this bundle is valid, in seconds since the unix epoch
        revertingTxHashes // (Optional) Array[String], A list of tx hashes that are allowed to revert
        replacementUuid   // (Optional) String, UUID that can be used to cancel/replace this bundle
    }]
}

Notes:

  • blockNumber can be:
    1. For a specific block: hex encoded block number (e.g. 0x1361bd3)
    2. For next block only: "0x" or null or missing field
  • uuid is supported as alias for replacementUuid.

Response ​

{
    "id": 1,
    "jsonrpc": "2.0",
    "result": {
        "bundleHash": "0x2228f5d8954ce31dc1601a8ba264dbd401bf1428388ce88238932815c5d6f23f"
    }
}

Example request ​

curl https://buildernet-flashbots-azure-eastus2-05.builder.flashbots.net \
    --cacert builder-cert.pem \  # or using --insecure
    --header 'Content-Type: application/json' \
    --header 'X-Flashbots-Signature: <public key address>:<signature>' \
    --data '{
        "id": 1,
        "jsonrpc": "2.0",
        "method": "eth_sendBundle",
        "params": [{
            "txs": [
                "0x000000..."
            ],
            "blockNumber": "0x1361bd3"
        }]
    }'

See this example Golang code for sending a transaction with a signed request and a pinned server certificate.

Replacing and cancelling bundles​

You can replace bundles by sending a new bundle with the same replacementUuid as the previous one. The new bundle will replace the old one.

If you want to cancel a bundle, you can send a new bundle with the same replacementUuid and an empty list of transactions.

Request signature and authentication ​

eth_sendBundle requests require a X-Flashbots-Signature header for authentication and for the signer to receive refunds:

X-Flashbots-Signature: <public_key_address>:<signature>

The signature is calculated by taking the EIP-191 hash of the json body encoded as UTF-8 bytes. Any valid ECDSA secp256k1 key (i.e. any Ethereum key) can be used to sign the payload. The address associated with this key will be used for Redistribution. For more details and examples on signing the payload, see the documentation here.

Instance TLS certificate ​

The builder node creates a fresh TLS certificate on each startup, of which the private key is guaranteed to stay inside the TEE instance. You can verify the TEE proof for this certificate using the "TEE Proof Validation API". You can also - insecurely - get the certificate with curl like this:

curl -w %{certs} -k https://buildernet-flashbots-azure-eastus2-05.builder.flashbots.net

Example Golang code ​

See this example Golang code for sending a signed transaction to a builder node. The example code supports requiring a specific TLS certificate as well as skipping certificate validation.

eth_sendRawTransaction​

You can use eth_sendRawTransaction to send a single signed transaction to BuilderNet.

Transactions sent this way are:

  • not sent to the mempool.
  • propagated to other BuilderNet builder nodes.
  • tried to include for up to 5 blocks.

Request ​

{
    "id": 1,
    "jsonrpc": "2.0",
    "method": "eth_sendRawTransaction",
    "params": ["0x000000..."]
}

Response ​

The response contains the transaction hash:

{
    "id": 1,
    "jsonrpc": "2.0",
    "result": "0x000000..."
}

Request signature and authentication ​

eth_sendRawTransaction requests also require a X-Flashbots-Signature header for authentication. For more details, see the relevant section for eth_sendBundle.

TEE Proof Validation API (aTLS)​

BuilderNet uses attested TLS (aTLS) to verify the attestation of specific builder node instances.

You can find more details in the Constellation docs:

aTLS modifies the TLS handshake by embedding an attestation statement into the TLS certificate. Instead of relying on a certificate authority, aTLS uses this attestation statement to establish trust in the certificate.

The protocol can be used by clients to verify a server certificate, by a server to verify a client certificate, or for mutual verification (mutual aTLS).

In BuilderNet, github.com/flashbots/cvm-reverse-proxy is responsible for attested TLS (aTLS) communication, both towards users as well as within the network. You can use the attested-get tool to receive the builder certificate over an attested channel:

# Install attested-get
go install github.com/flashbots/cvm-reverse-proxy/cmd/attested-get

# Get the builder certificate over an attested channel
attested-get \
    --addr=https://buildernet-flashbots-azure-eastus2-05.builder.flashbots.net:7936/cert \
    --expected-measurements=https://measurements.builder.flashbots.net \
    --out-response=builder-cert.pem

See also "Orderflow encryption and attestation" for more details.