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The eth_sendBundle method lets you group multiple signed transactions into a single atomic bundle and submit it directly to BlockRazor’s Block Builder. Because the Block Builder controls block construction, all transactions in a bundle are either included together in the exact order you specify or not at all—eliminating the risk of partial execution. This makes eth_sendBundle the preferred submission path for backrunning strategies, arbitrage bots, copy-trading systems, and any workflow where transaction ordering is critical.
New registered users can submit bundles to the Block Builder on BSC for free with no submission-rate limits. Sign up at https://blockrazor.io to get started.

​
Request Format

Send a standard JSON-RPC 2.0 POST request to the BlockRazor Block Builder endpoint with the method eth_sendBundle. 
{
  "jsonrpc": "2.0",
  "method": "eth_sendBundle",
  "params": [
    {
      "txs": ["0xSIGNED_TX_HEX_1", "0xSIGNED_TX_HEX_2"],
      "blockNumber": "0xE4E1C0",
      "minTimestamp": 0,
      "maxTimestamp": 0
    }
  ],
  "id": 1
}

​
Parameters

​
txs
array
required
An ordered array of signed transaction hex strings (RLP-encoded and prefixed with 0x). Transactions are included in the block in the exact order provided. All transactions must be valid and fully signed before submission.
​
blockNumber
string
required
The target block number, expressed as a hexadecimal string (e.g., "0xE4E1C0"). The bundle will only be considered for inclusion in this specific block. If the block is mined before your bundle is accepted, the bundle is discarded.
​
minTimestamp
integer
Optional Unix timestamp (seconds). The bundle will not be included in any block whose timestamp is earlier than this value. Set to 0 to disable the lower bound.
​
maxTimestamp
integer
Optional Unix timestamp (seconds). The bundle will not be included in any block whose timestamp is later than this value. Set to 0 to disable the upper bound.

​
Response Format

A successful submission returns a bundleHash that uniquely identifies your bundle within the Block Builder. You can use this hash with eth_traceBundle to retrieve execution details after the target block is mined. 
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "bundleHash": "0xABC123DEF456..."
  }
}
​
result.bundleHash
string
A hex string that uniquely identifies the submitted bundle. Retain this value to trace execution results via eth_traceBundle.

​
Example Integration

The following example builds a two-transaction bundle targeting a specific block and submits it using a standard HTTP client. 
const endpoint = "https://blockrazor.io/api/block-builder";

const bundle = {
  jsonrpc: "2.0",
  method: "eth_sendBundle",
  params: [
    {
      txs: [
        "0xSIGNED_TX_HEX_1",
        "0xSIGNED_TX_HEX_2",
      ],
      blockNumber: "0xE4E1C0",
      minTimestamp: 0,
      maxTimestamp: 0,
    },
  ],
  id: 1,
};

const response = await fetch(endpoint, {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    Authorization: "Bearer YOUR_API_KEY",
  },
  body: JSON.stringify(bundle),
});

const data = await response.json();
console.log("Bundle hash:", data.result.bundleHash);

​
Best Practices

1

Sign all transactions before bundling

Every entry in txs must be a fully signed, RLP-encoded raw transaction. The Block Builder will reject bundles that contain unsigned or malformed transactions.
2

Target the correct block number

Query eth_blockNumber immediately before building your bundle to get the latest block, then target latestBlock + 1. Bundles that miss their target block are silently discarded.
3

Simulate before submitting

Use eth_callBundle to simulate your bundle against the current state. Confirming profitability before live submission avoids wasted submissions and gas costs.
4

Retain the bundle hash

Store the returned bundleHash so you can call eth_traceBundle to verify execution and diagnose any issues after the target block is produced.
If your strategy requires lower submission latency, consider using Fast Submit in conjunction with eth_sendBundle to further reduce the time between bundle construction and Block Builder receipt.

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