Integration Guide

Submitting an End-of-Block Bundle

Use eth_sendEndOfBlockBundle with the same structure as a regular bundle. The only difference is the method name — the builder handles positioning automatically.

Python

import requests
from eth_account import Account

EUREKA_RPC = "https://rpc.eurekabuilder.xyz"

def send_end_of_block_bundle(signed_txs: list[str], block_number: int, private_key: str):
    body = {
        "jsonrpc": "2.0",
        "method": "eth_sendEndOfBlockBundle",
        "params": [{
            "txs": signed_txs,
            "blockNumber": hex(block_number),
        }],
        "id": 1,
    }

    # Sign the payload with Flashbots-style header
    message = json.dumps(body)
    account = Account.from_key(private_key)
    signature = account.sign_message(encode_defunct(text=message))
    header_value = f"{account.address}:{signature.signature.hex()}"

    response = requests.post(
        EUREKA_RPC,
        json=body,
        headers={"X-Flashbots-Signature": header_value},
    )
    return response.json()

JavaScript

curl

Replacing an End-of-Block Bundle

Use replacementUuid to update the bundle contents up until the block is built. Submit the same UUID with updated txs to replace the previously queued bundle. The builder always uses the latest version.

Python

import uuid

replacement_id = str(uuid.uuid4())

def send_replaceable_bundle(signed_txs, block_number, replacement_uuid, private_key):
    body = {
        "jsonrpc": "2.0",
        "method": "eth_sendEndOfBlockBundle",
        "params": [{
            "txs": signed_txs,
            "blockNumber": hex(block_number),
            "replacementUuid": replacement_uuid,
        }],
        "id": 1,
    }

    message = json.dumps(body)
    account = Account.from_key(private_key)
    signature = account.sign_message(encode_defunct(text=message))
    header_value = f"{account.address}:{signature.signature.hex()}"

    response = requests.post(
        EUREKA_RPC,
        json=body,
        headers={"X-Flashbots-Signature": header_value},
    )
    return response.json()

# Submit initial bundle
send_replaceable_bundle(["0x02f8..."], 20_400_000, replacement_id, private_key)

# Replace with updated transactions
send_replaceable_bundle(["0x02f9..."], 20_400_000, replacement_id, private_key)

JavaScript

curl

Cancelling

To cancel without submitting a replacement:

Python

def cancel_bundle(replacement_uuid, private_key):
    body = {
        "jsonrpc": "2.0",
        "method": "eth_cancelBundle",
        "params": [{
            "replacementUuid": replacement_uuid,
        }],
        "id": 1,
    }

    message = json.dumps(body)
    account = Account.from_key(private_key)
    signature = account.sign_message(encode_defunct(text=message))
    header_value = f"{account.address}:{signature.signature.hex()}"

    response = requests.post(
        EUREKA_RPC,
        json=body,
        headers={"X-Flashbots-Signature": header_value},
    )
    return response.json()

JavaScript

curl

Tracking Inclusion

End-of-block bundles return a bundleHash just like regular bundles. Use eureka_getBundleStats to track whether the bundle was included:

Python

def get_bundle_stats(bundle_hash, private_key):
    body = {
        "jsonrpc": "2.0",
        "method": "eureka_getBundleStats",
        "params": [{"bundleHash": bundle_hash}],
        "id": 1,
    }

    message = json.dumps(body)
    account = Account.from_key(private_key)
    signature = account.sign_message(encode_defunct(text=message))
    header_value = f"{account.address}:{signature.signature.hex()}"

    response = requests.post(
        EUREKA_RPC,
        json=body,
        headers={"X-Flashbots-Signature": header_value},
    )
    return response.json()

JavaScript

curl

With Refunds

End-of-block bundles support refundPercent and refundRecipient the same as regular bundles. The refund is calculated from the builder's profit attributable to the bundle.