How to Use Rabby Wallet Transaction Simulation Feature?

Rabby Wallet Transaction Simulation Overview

1. Rabby Wallet integrates a built-in transaction simulation engine that analyzes smart contract interactions before signing. This feature renders a deterministic preview of state changes, gas consumption, and potential reverts without broadcasting to the blockchain.

2. The simulation operates locally using an embedded EVM-compatible interpreter, eliminating reliance on external RPC endpoints for pre-execution checks.

3. Every transaction initiated through Rabby—whether token swaps, NFT mints, or contract calls—triggers automatic simulation unless explicitly disabled in advanced settings.

4. Simulated outcomes include balance deltas for all involved addresses, storage slot modifications, event emissions, and internal call traces mapped to source code locations when verified contracts are used.

5. Users receive immediate visual indicators: green checkmarks for safe operations, yellow warnings for high-gas or unusual permission grants, and red alerts for known exploit patterns or self-destruct triggers.

Enabling and Configuring Simulation Settings

1. Open Rabby Wallet extension and click the gear icon in the top-right corner to access Settings.

2. Navigate to the Security tab and locate Transaction Simulation toggle. Enable it to activate real-time previews.

3. Under Advanced Simulation Options, select whether to simulate only on mainnet, or extend to testnets including Sepolia, Arbitrum Sepolia, and Base Goerli.

4. Adjust Gas Threshold Warning to define custom limits—Rabby defaults to flagging any simulation exceeding 5 million gas units.

5. Toggle Contract Verification Enforcement to require Etherscan-verified source code before displaying human-readable function parameters and parameter risks.

Interpreting Simulation Results

1. After initiating a dApp transaction, Rabby displays a modal with three panels: Summary, Details, and Raw Trace.

2. The Summary panel highlights critical actions in green bold text: “Approves unlimited spending on USDC”, “Transfers 0.8 ETH to 0x7a…dF”, or “Calls setApprovalForAll on OpenSea proxy”.

3. The Details panel breaks down each internal call, showing exact input calldata, return values, and storage writes—including whether a slot previously held zero or non-zero value.

4. The Raw Trace panel exposes full EVM opcode execution flow, including JUMPDEST positions, memory writes, and stack depth—useful for auditors and developers verifying logic integrity.

5. A Revert Reason Preview appears if simulation detects failure paths, such as insufficient allowance, expired deadline, or missing signature—displayed in green bold text alongside the specific Solidity require statement causing it.

Limitations and Known Constraints

1. Simulation does not account for time-dependent variables like block.timestamp or block.number beyond current block context; future timestamps cannot be modeled accurately.

2. Contracts with external oracle calls or dynamic delegatecall targets may produce incomplete or inaccurate traces due to unresolvable external dependencies.

3. Gas estimation assumes static execution path; branches dependent on runtime conditions—such as msg.sender roles or governance votes—are simulated only along the default path unless manually overridden.

4. Multisig or threshold signature wallets interacting via relayers may show discrepancies between simulated and actual gas usage due to relay overhead not captured in local EVM.

5. No simulation covers consensus-level effects such as mempool front-running or sandwich attacks—those remain outside scope of client-side analysis.

Common Questions and Answers

Q: Does Rabby’s simulation work with custom RPC endpoints?A: Yes. Simulation runs independently of RPC selection. It uses local EVM state derived from your wallet’s current chain ID and block header—not the RPC provider’s response.

Q: Can I disable simulation for specific dApps?A: No. Rabby does not support per-site simulation toggles. Disabling applies globally across all connected applications and networks.

Q: Why does a transaction show ‘Simulation Passed’ but still revert on-chain?A: Common causes include race conditions where another transaction modifies shared state between simulation and broadcast, or reliance on off-chain data not available during local execution.

Q: Is simulation data stored or transmitted externally?A: Simulation is fully client-side. No calldata, addresses, or intermediate states leave the browser environment. All computation occurs within the extension’s isolated sandbox.