transaction-simulation

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title: "Transaction Simulation & Pre-Transaction Inspection"

Transaction Simulation & Pre-Transaction Inspection

Before signing any on-chain transaction, it’s vital to simulate and inspect exactly what will happen. Transaction previews are your last line of defense against scams, drainers, and accidental mistakes.

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Why Simulate Transactions?

• Hidden Functionality: Malicious contracts can mask draining actions inside harmless-looking UI screens.
• Accidental Risk: Even legitimate apps might send unexpected calls without clear warning.
• Gas and Fees Visibility: See true gas costs and side effects before committing funds.

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Core Simulation Methods

1. Wallet Previews

• MetaMask Simulation: MetaMask displays a summary of balance changes and function names.
• Limitations:
  • Only shows superficial details.
  • Complex internal calls (multicalls, delegatecalls) may not be fully visible.

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2. Advanced Simulation Tools

Use dedicated simulators to inspect complete transaction flows:

• Tenderly Simulation:
  • Paste transaction hex and simulate state changes.
  • Shows contract storage diffs, emitted events, and internal call trees.
• Rabby Wallet:
  • Transaction simulation built into the wallet UI.
  • Detects if an approval also triggers hidden transferFrom() calls.
• DeBank Simulation:
  • Preview expected token balance changes post-transaction.

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3. Manual Dry-Run on Forked Network

For high-value transactions, simulate manually on a mainnet fork:

npx hardhat node --fork https://mainnet.infura.io/v3/YOUR_INFURA_KEY

• Impersonate your address:

  await hre.network.provider.request({
    method: "hardhat_impersonateAccount",
    params: ["0xYourAddress"]
  });
• Send the transaction manually and review resulting changes:
  • Token balances
  • Smart contract storage
  • Emitted events

This is the closest method to a real-world “testnet” for your personal transaction.

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Red Flags During Simulation

Red Flag	What It Means
Unauthorized Token Transfers	Contract could steal your tokens after approval
Unexpected State Changes	Contract modifies storage beyond what you intended
Selfdestruct Call	Contract destroys itself, seizing attached funds
Approve & Transfer in Same Tx	Classic drainer exploit

Always investigate unexpected behavior before proceeding.

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Tools Summary

• Tenderly — Full transaction simulation with internal call tree.
• Rabby Wallet — Inline simulation and risk alerting.
• DeBank — Basic post-tx balance prediction.
• Hardhat / Foundry — Local fork simulation for technical users.

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Conclusion

Transaction simulation transforms signing from guesswork into knowledge.
When every transaction is simulated beforehand, your odds of getting phished, drained, or rug-pulled drop dramatically.

Even one saved transaction justifies the effort.

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Next Steps

After mastering simulation, move to Module 4.4: Revoke.cash Guide & Managing Approvals to clean up risky allowances and harden your wallet even further.

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