Multi-Transaction Bundle Simulator

WHAT IT DOES

Multi-Transaction Bundle Simulator is a specialized developer and security tool that simulates bundles of multiple Ethereum transactions without broadcasting them to the network. It uses eth_call to execute each transaction against the current chain state sequentially, providing a preview of what would happen if the entire bundle were sent. The tool reads each target contract's bytecode via eth_getCode to verify deployment, retrieves the current chain state and block number for context, and checks the wallet's balance for cumulative gas estimation. It parses each transaction's calldata and simulates execution, returning the result data, per-transaction gas usage estimates, and cumulative gas costs for the entire bundle. The tool also decodes return values using contract ABIs when available, and provides a detailed breakdown of each transaction's status, gas usage, return value, and any reverts or errors. All of this is performed read-only and off-chain, giving users a clear understanding of how a sequence of transactions would interact before they sign and broadcast any of them.

HOW TO USE

Connect your wallet to the target EVM chain. Enter up to three transactions to simulate: for each, provide the contract address, the calldata (hex-encoded, 0x-prefixed), and optionally the ETH value to send. Click "Simulate bundle" to run the simulation. The tool will execute each transaction sequentially using the current chain state, applying state changes from earlier transactions to later ones in the bundle. Results include: overall status (all succeeded or some failed), per-transaction success/failure indicators, gas estimates for each transaction, cumulative gas total, return values from each call, and a validation summary of all checks performed. This helps you understand how a sequence of contract interactions will behave before committing to the gas costs and potential side effects.

TECHNICAL NOTE: SEQUENTIAL SIMULATION AND CUMULATIVE STATE

The tool performs a multi-stage simulation process that runs each transaction in sequence, applying the state changes from each successful transaction to the context of the next. This mimics the behavior of an actual bundle where transactions are executed in order. For each transaction, the tool first verifies the target contract has deployed bytecode using eth_getCode. It then performs gas estimation using eth_estimateGas, which returns the gas required for that specific transaction to succeed. The tool then executes the transaction using eth_call with the same parameters, which runs the transaction against the current state without modifying it. This call returns the output data from the function execution. The tool tracks cumulative gas costs across all transactions, providing a total gas estimate for the bundle. It also checks the wallet balance and compares it against the cumulative estimated gas cost to predict whether the entire bundle can be successfully broadcast. All RPC calls are chunked and backed off automatically to handle varying provider rate limits.

WHAT IT CANNOT SEE

The tool cannot simulate transactions that require specific signature validation (e.g., EIP-712 signed messages) or off-chain dependencies like API calls, as these are not available in the simulation environment. It cannot predict transaction ordering or MEV impacts within the bundle, since the simulation runs in isolation without the mempool context. It cannot simulate state changes from pending transactions in the mempool, as eth_call only reflects the current confirmed state. It cannot detect reentrancy or cross-contract attacks that depend on live execution context, as these may only manifest during actual broadcast. The tool cannot simulate bundles on non-EVM chains. It cannot verify that the simulation results match actual execution if chain state changes between simulation and broadcast, as blocks may be mined in the interim. It cannot simulate bundles that require gas price or priority fee dynamics accurately, as these are determined by network conditions at broadcast time. It cannot guarantee that all transactions in the bundle will succeed when broadcast together, as state changes from earlier transactions may affect later ones differently than simulated.

PLEASE NOTE

This tool is designed exclusively for EVM-compatible chains (Ethereum, Polygon, BSC, Arbitrum, Optimism, Avalanche C-Chain, etc.). It does not support non-EVM blockchains like Bitcoin, Solana, Cosmos, or Tron. This is a read-only simulation tool and does not submit any transactions to the network. Simulation results are based on the current block state and may change if the chain state advances between simulation and broadcast. The tool simulates up to 3 transactions per bundle. For larger bundles, consider splitting into multiple simulations. Always perform simulations close to the time of intended broadcast for best accuracy. The tool provides no warranty or guarantee of transaction success; users are responsible for verifying simulation results and understanding the implications of their transactions before signing and broadcasting.