Bundle Mode: Atomic Block-Level Transaction Execution

BlockRazor’s Bundle mode allows you to submit a group of transactions that must land atomically — all in the same block, in a defined order, immediately following a “signal transaction” of interest. If any transaction in the bundle fails or the ordering cannot be satisfied, the entire bundle is discarded. This guarantee makes Bundle mode the standard tool for sophisticated strategies such as backrunning DEX swaps, copy trading on-chain activity, and token sniping at launch.

Two Roles in the Bundle Ecosystem

Bundle mode is designed around two distinct participant types, each with different responsibilities and API methods:

Project Builder

Project Builders submit bundles of signed transactions to be included atomically in the next block. They target a specific block and define the full set of transactions to execute in order.

Searcher

Searchers participate in BlockRazor’s orderflow auction by placing bids. They compete to have their transactions included alongside signal transactions by offering the highest bid to the block builder.

Supported Chains

BSC

Project Builders: eth_sendMevBundle
Searchers: eth_sendMevBundle (bid variant)
No rate limits for new registered users.

Ethereum

Project Builders: eth_sendBundle
Searchers: eth_sendBid
No rate limits for new registered users.

Submitting a Bundle

BSC
Ethereum

Project Builder
Searcher

BSC Project Builders use eth_sendMevBundle to submit an ordered list of signed transactions targeting a specific block number.

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "eth_sendMevBundle",
  "params": [{
    "txs": ["0xSIGNED_TX_1", "0xSIGNED_TX_2"],
    "blockNumber": "0xE4E1C0"
  }],
  "id": 1
}

cURL

curl -X POST https://bundle.blockrazor.io/bsc \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_AUTH_TOKEN' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendMevBundle",
    "params": [{
      "txs": ["0xSIGNED_TX_1", "0xSIGNED_TX_2"],
      "blockNumber": "0xE4E1C0"
    }],
    "id": 1
  }'

ethers.js

import { ethers } from "ethers";

const provider = new ethers.JsonRpcProvider(
  "https://bundle.blockrazor.io/bsc?auth=YOUR_AUTH_TOKEN"
);

const wallet = new ethers.Wallet("YOUR_PRIVATE_KEY", provider);

// Get the current block number and target the next block
const currentBlock = await provider.getBlockNumber();
const targetBlock = currentBlock + 1;

// Sign your transactions
const tx1 = await wallet.signTransaction({
  to: "0xCONTRACT_ADDRESS",
  data: "0xCALLDATA_TX1",
  gasLimit: 200000,
  maxFeePerGas: ethers.parseUnits("5", "gwei"),
  maxPriorityFeePerGas: ethers.parseUnits("1", "gwei"),
  nonce: await wallet.getNonce(),
  chainId: 56,
  type: 2,
});

const tx2 = await wallet.signTransaction({
  to: "0xCONTRACT_ADDRESS",
  data: "0xCALLDATA_TX2",
  gasLimit: 150000,
  maxFeePerGas: ethers.parseUnits("5", "gwei"),
  maxPriorityFeePerGas: ethers.parseUnits("1", "gwei"),
  nonce: (await wallet.getNonce()) + 1,
  chainId: 56,
  type: 2,
});

// Send the bundle
const result = await provider.send("eth_sendMevBundle", [
  {
    txs: [tx1, tx2],
    blockNumber: "0x" + targetBlock.toString(16),
  },
]);

console.log("Bundle submitted:", result);

txs

string[]

required

Array of signed, RLP-encoded transactions in hex format. They will be executed in order.

blockNumber

string

required

The target block number in hexadecimal. The bundle is only valid for this exact block.

minTimestamp

number

Optional Unix timestamp (seconds). The bundle will not be included before this time.

maxTimestamp

number

Optional Unix timestamp (seconds). The bundle will not be included after this time.

Searchers on BSC use the eth_sendMevBundle bid variant to participate in BlockRazor’s orderflow auction. A bid specifies the signal transaction to backrun and the maximum amount the searcher is willing to pay.

cURL

curl -X POST https://bundle.blockrazor.io/bsc \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_AUTH_TOKEN' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendMevBundle",
    "params": [{
      "txs": ["0xSIGNED_SEARCHER_TX"],
      "blockNumber": "0xE4E1C0",
      "revertingTxHashes": [],
      "maxBid": "0x2386F26FC10000"
    }],
    "id": 1
  }'

Searchers compete in an auction. A higher maxBid increases the probability of your bundle being selected by BlockRazor’s Block Builder. The actual amount charged is the clearing price, not necessarily the max bid.

Project Builder
Searcher

Ethereum Project Builders use eth_sendBundle following the standard Flashbots bundle specification.

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "eth_sendBundle",
  "params": [{
    "txs": ["0xSIGNED_TX_1", "0xSIGNED_TX_2"],
    "blockNumber": "0x14A5B60"
  }],
  "id": 1
}

cURL

curl -X POST https://bundle.blockrazor.io/ethereum \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_AUTH_TOKEN' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendBundle",
    "params": [{
      "txs": ["0xSIGNED_TX_1", "0xSIGNED_TX_2"],
      "blockNumber": "0x14A5B60"
    }],
    "id": 1
  }'

ethers.js

import { ethers } from "ethers";

const provider = new ethers.JsonRpcProvider(
  "https://bundle.blockrazor.io/ethereum?auth=YOUR_AUTH_TOKEN"
);

const wallet = new ethers.Wallet("YOUR_PRIVATE_KEY", provider);

const currentBlock = await provider.getBlockNumber();
const targetBlock = currentBlock + 1;

const tx1 = await wallet.signTransaction({
  to: "0xCONTRACT_ADDRESS",
  data: "0xCALLDATA_TX1",
  gasLimit: 250000,
  maxFeePerGas: ethers.parseUnits("30", "gwei"),
  maxPriorityFeePerGas: ethers.parseUnits("2", "gwei"),
  nonce: await wallet.getNonce(),
  chainId: 1,
  type: 2,
});

const result = await provider.send("eth_sendBundle", [
  {
    txs: [tx1],
    blockNumber: "0x" + targetBlock.toString(16),
  },
]);

console.log("Ethereum bundle submitted:", result);

txs

string[]

required

Array of signed, RLP-encoded transactions in hex format.

blockNumber

string

required

Target block number in hexadecimal. The bundle is valid only for this block.

revertingTxHashes

string[]

Optional list of transaction hashes that are allowed to revert without invalidating the entire bundle.

Searchers on Ethereum use eth_sendBid to place auction bids in BlockRazor’s orderflow system.

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "eth_sendBid",
  "params": [{
    "txs": ["0xSIGNED_SEARCHER_TX"],
    "blockNumber": "0x14A5B60",
    "bid": "0x11C37937E08000"
  }],
  "id": 1
}

cURL

curl -X POST https://bundle.blockrazor.io/ethereum \
  -H 'Content-Type: application/json' \
  -H 'Authorization: Bearer YOUR_AUTH_TOKEN' \
  -d '{
    "jsonrpc": "2.0",
    "method": "eth_sendBid",
    "params": [{
      "txs": ["0xSIGNED_SEARCHER_TX"],
      "blockNumber": "0x14A5B60",
      "bid": "0x11C37937E08000"
    }],
    "id": 1
  }'

txs

string[]

required

Array of signed searcher transactions to include in the bundle.

blockNumber

string

required

Target block number in hexadecimal.

bid

string

required

The bid amount in wei (hex). This is the maximum the searcher will pay for block inclusion.

eth_sendBid participates in a sealed-bid auction. Bids are evaluated by BlockRazor’s Block Builder to determine which bundles maximize block value. Searchers with winning bids pay the clearing price.

Common Use Cases

Backrunning

Submit a transaction immediately after a large DEX swap to capture arbitrage from the resulting price impact.

Copy Trading

Mirror the transactions of a target wallet atomically in the same block, executing the same trades at the same prices.

Token Sniping

React to a liquidity addition or token launch by bundling your buy transaction to land in the same block as the signal.

BlockRazor’s Block Builder on BSC has a historical cumulative block production rate of 37%, ranking first on the BSC chain. High builder share means higher probability of your bundle landing in the target block. View live stats at Dune Analytics.

API Reference

BSC — Project Builder

Full eth_sendMevBundle schema for BSC Project Builders.

BSC — Searcher

Auction bid parameters for BSC Searchers.

Ethereum — Project Builder

Full eth_sendBundle schema for Ethereum Project Builders.

Ethereum — Searcher

eth_sendBid parameters for Ethereum Searchers.

Get Started

Use Cases

Transaction Submission

Streams

Block Builder

Bundle Mode: Atomic Block-Level Transaction Execution

Two Roles in the Bundle Ecosystem

Project Builder

Searcher

Supported Chains

BSC

Ethereum

Submitting a Bundle

JSON-RPC Request

cURL

ethers.js

cURL

JSON-RPC Request

cURL

ethers.js

JSON-RPC Request

cURL

Common Use Cases

Backrunning

Copy Trading

Token Sniping

API Reference

BSC — Project Builder

BSC — Searcher

Ethereum — Project Builder

Ethereum — Searcher

Build docs developers (and LLMs) love

Get Started

Use Cases

Transaction Submission

Streams

Block Builder

Documentation Index

​Two Roles in the Bundle Ecosystem

Project Builder

Searcher

​Supported Chains

BSC

Ethereum

​Submitting a Bundle

​JSON-RPC Request

​cURL

​ethers.js

​cURL

​JSON-RPC Request

​cURL

​ethers.js

​JSON-RPC Request

​cURL

​Common Use Cases

Backrunning

Copy Trading

Token Sniping

​API Reference

BSC — Project Builder

BSC — Searcher

Ethereum — Project Builder

Ethereum — Searcher

Build docs developers (and LLMs) love

Two Roles in the Bundle Ecosystem

Supported Chains

Submitting a Bundle

JSON-RPC Request

cURL

ethers.js

cURL

JSON-RPC Request

cURL

ethers.js

JSON-RPC Request

cURL

Common Use Cases

API Reference