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The eth_callBundle method simulates the execution of a bundle against a specified BSC chain state without submitting any transactions on-chain. This gives you a gas-free, risk-free way to verify that your bundle will execute as intended before committing to eth_sendBundle. The response provides per-transaction results including gas consumed, return values, and revert reasons, enabling your system to catch errors and optimize gas parameters before they cost real funds.
Bundle simulation via eth_callBundle is available to registered users on BSC. See Pricing for subscription tier details.

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Endpoint

POST https://builder.blockrazor.io/bsc
Authentication is performed via a Bearer token passed in the Authorization header.

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Request

The request follows the standard JSON-RPC 2.0 envelope. The single element of params is a simulation configuration object.

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Simulation Parameters

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txs
string[]
required
An ordered array of signed raw transactions encoded as hex strings (each prefixed with 0x). The transactions are simulated in the order provided against the specified chain state, mirroring how they would execute if submitted as a live bundle.
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blockNumber
string
required
The block number against which the bundle is simulated, expressed as a hex string (e.g., "0xE4E1C0"). This controls which block context (base fee, block hash, coinbase) the simulation uses.
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stateBlockNumber
string
required
The block number or the string "latest" that determines which world state snapshot is used during simulation. Use "latest" to simulate against the current chain tip, or specify a historical block number to replay against past state.
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timestamp
integer
Optional. A Unix timestamp override (in seconds) to use as the simulated block’s timestamp. Useful for testing time-dependent logic such as TWAP calculations or time-locked contracts.

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Code Examples

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

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Response

The response contains the bundle hash and an array of per-transaction simulation results. Each entry in results corresponds to a transaction in the input txs array, in the same order.
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bundleHash
string
A hash derived from the simulated bundle. This value matches the hash that would be returned by eth_sendBundle if you submit the same bundle, allowing you to correlate simulation results with live submissions.
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results
object[]
An array of simulation result objects, one per transaction in the input txs array.
Response Example
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "bundleHash": "0x7f3a9c2e1d4b...",
    "results": [
      {
        "txHash": "0xabc123...",
        "gasUsed": 84200,
        "value": "0x0000000000000000000000000000000000000000000000000de0b6b3a7640000"
      },
      {
        "txHash": "0xdef456...",
        "gasUsed": 61500,
        "value": "0x",
        "error": "execution reverted: insufficient output amount"
      }
    ]
  }
}

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Interpreting Simulation Results

Each entry in results maps directly to the corresponding transaction in your txs input. A missing error field indicates the transaction succeeded. An error field with a revert message indicates the transaction would revert under the simulated conditions.
Simulation results reflect the state at stateBlockNumber, not necessarily the state at the block when you submit a live bundle. Chain state may change between simulation and actual block building, particularly for DeFi positions sensitive to price movements. Re-simulate close to the time of submission for the most accurate results.
If gasUsed from simulation is close to your transaction’s gas limit, increase the gas limit before live submission. Blocks include a small amount of overhead beyond pure simulation gas, and running out of gas on-chain causes a revert that consumes all provided gas.

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