What Is a Crypto Transaction Simulation? A Guide to Checking Your Balance, Permissions, and Risks Before Signing Your Wallet

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Crypto transaction simulation is a security and analysis method that attempts to show the estimated result by running a transaction in a virtual environment before sending it to the blockchain.

A good transaction preview can show you:

• which token or NFT will be sent from the wallet,
• which asset will be received into the wallet,
• whether there is a risk of the transaction failing,
• which smart contract is being interacted with,
• whether permission to spend the token is being granted,
• Is an unlimited approval being requested,
• Is bulk authorization granted for the NFT collection,
• what is the estimated gas fee,
• is the transaction a simple transfer or a complex smart contract call?

However, the simulation is not guaranteed. The blockchain state may change, prices may fluctuate, MEV effects may occur, liquidity may decrease, or a malicious contract may behave differently during the simulation than it does in a real transaction.

Who is this guide for?

This guide is for:

• Users of MetaMask, Rabby, Trust Wallet, Coinbase Wallet, or other personal wallets,
• Those planning to perform swap, stake, bridge, or claim transactions on a DeFi platform,
• Those who see unreadable data on their wallet screen,
• Those who receive “Approve,” “Permit,” “SetApprovalForAll,” or “Sign” prompts,
• those who want to protect themselves from wallet drainer attacks,
• those who want to understand which tokens will be issued before a transaction,
• those who want to manage risk during NFT minting or airdrop claims,
• those approving transactions in a multisig or corporate wallet,
• and advanced users who want to use Tenderly or similar simulators

.

Critical Risk Warning

Viewing a transaction simulation does not guarantee that the transaction is absolutely secure.

The transaction should be stopped in the following situations:

• If the simulation shows an unexpected token outflow from your wallet,
• if an NFT transfer is detected,
• if unlimited token permission is requested,
• if setApprovalForAll permission is granted for the entire NFT collection,
• if the transaction result cannot be read,
• if the site asks for a seed phrase or private key,
• if the transaction appears to be a “reward claim” but requests access to USDC, USDT, WETH, or NFTs,
• if the information on the transaction confirmation and signature screens does not match,
• if the site prompts “Continue” even though the simulation fails.

No transaction preview tool should ever ask for a seed phrase or private key.

What is a crypto transaction simulation?

A transaction simulation is a method of running a blockchain transaction on the current chain state for testing purposes before sending it to the live network.

Real transaction: Sign → send to the network → processed in a block → result is finalized Simulation: Test transaction data → display estimated result → user makes a decision

Simulation tools seek to answer the following question:

Sample result:

Output: - 100 USDC - 0.002 ETH gas Future: - 99.4 USDT Additional risk: - No new token approval - No NFT transfer

Risky example:

Output: - Transfer permission for the entire NFT collection Result: - No assets visible Risk: - setApprovalForAll transaction

Is the wallet approval screen the same as the simulation?

They are not exactly the same.

Wallet approval screen

Displays basic information about the transaction or message the wallet will ask you to sign:

• the network the transaction is on,
• gas fee,
• contract address,
• the local coin to be sent,
• the function being called,
• message to be signed.

Transaction simulation

It attempts to predict the expected result if the transaction is executed:

• which token will be issued,
• which token will be received,
• which NFT will be transferred,
• how the balance will change,
• could the transaction fail,
• which internal calls will the contract make?

The safest approach is to review both together. The wallet confirmation screen answers the question “What am I signing?”, while the simulation answers “What happens if I sign?”

In which transactions is the simulation useful?

Token transfer

Expected:

• the tokens being sent,
• amount sent,
• recipient address,
• gas fee.

Risk scenario:

• different token output,
• unexpected additional transfer,
• recipient address has changed.

Swap

Expected:

• token sold,
• minimum tokens to be received,
• slippage,
• DEX or router address,
• gas fee.

Risk scenario:

• the number of tokens received is much lower than expected,
• receipt of counterfeit tokens,
• a different contract call,
• requesting unlimited approval first.

Token approval

Expected:

• which token is authorized,
• which spender address is authorized,
• the amount of authorization.

Risky scenario:

• unlimited USDT, USDC, or WETH authorization,
• unknown spender,
• authorization for a token that will not be used in a transaction,
• requesting approval only for a transaction believed to be a claim.

NFT transactions

Expected: a specific NFT mint or transfer.

Risky scenario:

• `setApprovalForAll` for the entire collection,
• NFT transfer permission,
• withdrawal of existing NFTs from the wallet,
• loss of an NFT in a transaction that appears to be a free mint.

Bridge

Expected:

• token withdrawal from the source network,
• corresponding asset on the destination network,
• bridge contract,
• estimated duration,
• fees.

Risk scenarios:

• incorrect bridge contract,
• unexpected asset on the target network,
• high fee,
• low minimum output,
• fake bridge website.

Staking

Expected: token to be staked, lock-up period, unstake condition, and reward token.

Risky scenarios: transfer instead of staking, non-reversible contract, unlimited token permissions, or high early exit penalty.

Airdrop Claim

Expected: token to be claimed, low gas fee, and official contract.

Risky scenarios: stablecoin withdrawal, NFT transfer, permit signature, unlimited approval, or a contract not belonging to the site.

Which fields should be reviewed on the simulation screen?

1. Network

On which network is the transaction taking place? Is the network selection correct (e.g., Ethereum, Base, Arbitrum, Optimism, Polygon, BNB Smart Chain, Avalanche, or Solana)?

2. Interacted Contract

Check:

• the contract address,
• explorer tag,
• verified code,
• address in the official documentation,
• previously used protocol addresses.

3. Outgoing assets

Be sure to check:

• Native coins such as ETH, BNB, and SOL,
• stablecoins such as USDT, USDC, and DAI,
• High-value tokens like WETH and WBTC,
• NFTs,
• LP tokens,
• staking tokens.

4. Future Assets

Check whether the incoming token is genuine, whether the token contract is official, whether it has liquidity, and whether it is a counterfeit token.

5. Approval or permit

• token name,
• spender address,
• permission amount,
• is it unlimited,
• for a single transaction,
• Permit2 or a similar batch permission system?

6. NFT permission

The following statements may be critical:

• setApprovalForAll
• approve
• operator
• all assets
• collection approval

7. Gas fee

The estimate may not reflect the final fee. Gas may be spent even if the transaction fails.

8. Failure warning

Possible causes:

• insufficient balance,
• insufficient allowance,
• slippage,
• contract paused,
• timeout,
• wrong network,
• invalid signature,
• token transfer restriction,
• honeypot behavior.

What does the simulation not guarantee?

The block state may change

Liquidity, price, and contract status at the time of the simulation may change before the transaction is added to the block.

Slippage may occur

In swap transactions, the actual outcome may differ from the expected outcome.

MEV effects may occur

The order in which transactions are executed may alter the price or outcome.

A harmful contract may behave differently

Some contracts may behave differently depending on the specific user, block, time, or transaction context.

Does not verify token value

The simulation may display the incoming token; however, it does not guarantee that the token has actual market value.

Does not prevent social engineering

If a user knowingly signs a transaction on a fake site, the simulation can only issue a warning.

It may not always be able to fully analyze message signatures

Some off-chain signatures may later be converted into on-chain transactions. Permit and structured signatures require special attention.

Why is a Permit signature particularly important?

Permit allows a user to grant authorization to spend tokens via a signature without sending an on-chain approve transaction.

Things to check:

• which token the permit is granted for,
• who is the spender,
• what is the amount of the permit,
• Is there an expiration date,
• Is the nonce correct?
• Which domain is the signature for,
• Is the site official,
• is the signature readable?

Why is `setApprovalForAll` dangerous?

In NFT standards, `setApprovalForAll` can grant an operator the authority to manage all NFTs in the relevant collection.

You think you’re minting an NFT. But your wallet is actually granting transfer permissions for the entire collection.

Even if no NFT is immediately transferred in the transaction, the authorization may remain in effect.

How to use the transaction simulator step by step?

Step 1: Verify the site

Check the domain name, do not access it via an ad link, and verify it using the official documentation.

Step 2: Select the correct network

The network selected in your wallet must match the network you want to use for the transaction.

Step 3: Initiate the transaction but do not sign it immediately

In the wallet window, review the transaction type, recipient or contract address, gas fee, data field, and warnings.

Step 4: Review the simulation results

• Tokens to be issued,
• incoming tokens,
• NFT movements,
• approval changes,
• failure warning.

Step 5: Check the contract address on the blockchain explorer

Do not sign high-value transactions to unknown contracts.

Step 6: Consider token permissions separately

Instead of granting unlimited permissions, grant permissions only for the transaction amount if possible.

Step 7: Run a small test

Before making a high-value transaction, perform a small swap, transfer, bridge, or use a separate test wallet.

Step 8: Check the blockchain explorer after the transaction

Review the TXID, token transfers, event logs, approval records, and NFT movements.

What tools are available?

In-wallet transaction preview

Some modern wallets display the transaction result directly on the confirmation screen.

Advantage: User-friendly and fast.

Limitation: Supported networks may be limited; complex transactions may not be fully resolved, and a centralized simulation server may compromise privacy.

MetaMask estimated balance changes

MetaMask may display estimated balance changes for some transactions. Since transaction data may be sent to a central server for simulation, privacy settings should be evaluated.

Rabby transaction simulation

Rabby aims to clearly display the expected token and NFT changes before a transaction. It does not guarantee the outcome.

Tenderly Simulator

For more technical users, it offers transaction simulation, smart contract monitoring, and debugging tools.

Explorer and transaction decoding tools

Transaction data, event logs, and contract calls can be examined in Etherscan-like explorers.

Does simulation pose a privacy risk?

Yes. When a transaction is simulated, the following information may be sent to a third-party server:

• wallet address,
• IP address,
• transaction data,
• the contract being interacted with,
• token information,
• estimated transaction intent.

Users concerned about privacy should evaluate the simulation provider, its data policy, the ability to disable the setting, and the option to use a local/self-hosted node.

How can a wallet drainer be detected in a simulation?

Red flags:

• Outflows of USDT, USDC, or WETH from the wallet,
• NFT transfers,
• `setApprovalForAll`,
• unlimited approval,
• Permit2 permission,
• unknown contract,
• no incoming assets,
• transaction description does not match the balance change,
• token spending permission instead of an airdrop claim.

The user should ask:

What should be done if the simulation appears to have failed?

If the simulation fails, the transaction should not be sent.

Possible reasons:

• insufficient gas,
• insufficient token balance,
• missing approval,
• slippage is too low,
• expired,
• contract is paused,
• user is not on the whitelist,
• minting is complete,
• no bridge liquidity,
• wrong network,
• RPC error,
• the contract is intentionally reverting.

Troubleshooting steps:

1. Take note of the transaction details.
2. Check your wallet’s network.
3. Check your balance and gas status.
4. Check if token approval is required.
5. Don’t set the slippage limit too high.
6. Review the protocol’s official status page.
7. Check the contract on the blockchain explorer.
8. If necessary, run a small test.
9. If you’re still unsure, cancel the transaction.

Checks to perform even if the simulation results appear safe

• Is the site official?
• Is the network correct?
• Is the wallet address correct?
• Is the contract address official?
• Are the tokens being issued as expected?
• Are the upcoming tokens as I expected?
• Is there an NFT release?
• Is approval granted?
• Is the permission unlimited?
• Is the gas fee reasonable?
• Is the transaction amount high?
• Should a test transaction be performed?
• Will the permission need to be revoked after the transaction?

Red flags before the transaction

• The “Free Reward” transaction removes tokens from the wallet.
• The “Verify wallet” transaction requires NFT permission.
• The “Claim” transaction requires stablecoin approval.
• The site is asking for your seed phrase.
• The signature data cannot be read.
• The wallet is displaying a warning, but the site tells you to dismiss it.
• The simulation failed, but the site is asking you to continue.
• The transaction contract is new and unverified.
• There is a phishing warning for the contract in the explorer.
• The contract for the token you’re receiving isn’t official.
• It says the transaction must be completed immediately.
• There’s pressure to act within “the last 5 minutes.”
• A support agent is guiding you via screen sharing.

Practical Scenarios

Scenario 1: The airdrop claim process requires USDC approval

Expectation: To claim free tokens.

Simulation: 0 tokens are received, and unlimited spending permission is granted for USDC.

Actions:

1. Reject the transaction.
2. Close the site.
3. Disconnect the wallet.
4. If you’ve signed before, check your permissions.
5. If necessary, transfer the assets to a clean wallet.

Scenario 2: The NFT mint transaction requests permission for the entire collection

The minting process should not request permission to manage your existing NFTs. The transaction should be rejected.

Scenario 3: The swap shows a result significantly lower than expected

Expected: Approximately 3,500 USDC in exchange for 1 ETH.

Simulation: 1 ETH is sent out, 2,100 USDC is received.

Possible causes: wrong token, low liquidity, high slippage, fake pool, or price manipulation.

Scenario 4: Gas is not visible on the target network during a bridge transaction

Even if the token reaches the target network, local gas coins may be required to execute transactions on that network.

Scenario 5: A multisig treasury transaction is directed to an unknown contract

If the simulation shows a call to an unknown contract when a USDC payment is expected, the proposal should be rejected.

Scenario 6: The simulation shows no changes but a signature is requested

Even if there is no balance change, the signed message may contain a permit or authorization. The domain and message content must be checked.

Troubleshooting Table

Security Checklist

• ☐ I verified the site’s domain name.
• ☐ I checked the network where the transaction will take place.
• ☐ I read the wallet confirmation screen.
• ☐ I checked the assets that will appear in the simulation.
• ☐ I checked the assets that will be received in the simulation.
• ☐ I checked whether there is an NFT transfer.
• ☐ I checked for any approvals or permits.
• ☐ I rejected or limited any unlimited permissions.
• ☐ I checked the spender contract on the blockchain explorer.
• ☐ I verified the token contract from an official source.
• ☐ I reviewed the gas fee and the risk of failure.
• ☐ My transaction expectations match the simulation results.
• ☐ I considered a high-value test transaction.
• ☐ I rejected any unreadable signatures.
• ☐ I did not share my seed phrase or private key.
• ☐ I will verify the TXID after the transaction.
• ☐ I will revoke token permissions if necessary.

Frequently Asked Questions

What is a crypto transaction simulation?

A transaction simulation is a method of running a crypto transaction virtually—before sending it to the live network—to show estimated changes in balance, tokens, NFTs, and gas fees.

Are the simulation results definitive?

No. The block state, liquidity, price, MEV, and smart contract behavior may change before the transaction is executed.

If the simulation shows the transaction is safe, is the transaction definitely safe?

No. The simulation is an auxiliary security layer; the official website, contract address, token permissions, and signature content must also be verified.

What are MetaMask estimated balance changes?

It is a transaction preview feature in MetaMask that attempts to display estimated balance changes for certain transactions.

What does Rabby transaction simulation do?

It attempts to show the expected token and NFT changes before the transaction is signed.

Who is the Tenderly Simulator suitable for?

It is suitable for more technical users, developers, teams approving multisig transactions, and those who want to examine DeFi transactions in detail.

Why is a "Permit" signature risky?

A "Permit" signature can grant permission to spend tokens without sending an on-chain approve transaction. Even a signature that doesn’t require gas can be risky.

What does `setApprovalForAll` mean?

It can grant governance authority to a specific operator for all assets in an NFT collection.

Should the transaction be executed if the simulation fails?

Generally, no. The reason for the failure should be understood first.

Does the simulation pose a privacy risk?

Yes. Some features may send transaction data and IP addresses to centralized simulation servers.

How can a wallet drainer be detected in a simulation?

Unexpected token or NFT outflows, unlimited approvals, `permit`, `setApprovalForAll`, or the absence of incoming assets are strong risk indicators.

Is simply signing a message safe?

Not always. Some message signatures may include authorizations or permits.

Conclusion

Crypto transaction simulation is one of the most practical layers of security for wallets. It aims to show the user not only “which button they clicked,” but also what will change in their wallet if the transaction goes through.

The transaction preview should be read carefully, especially before airdrop claims, NFT mints, token approvals, swaps, bridges, staking, and multisig treasury transactions.

The safest approach:

1. Verify the site,
2. check the network,
3. read the wallet confirmation screen,
4. review the simulation result,
5. distinguish between approval and NFT permissions,
6. verify the contract address,
7. perform high-value test transactions,
8. and checking post-transaction permissions and the TXID.

If the simulation result does not match your transaction expectations, the best course of action is to reject the transaction.

Related Safety Guides

• USDT network selection guide
• wrong-network recovery guide
• memo and destination tag guide