Transaction Simulation

Transaction simulation is a wallet or security-tool feature that runs a proposed transaction against a copy of current chain state before you sign it, then shows the balance and approval changes it would produce. It turns an opaque blob of calldata into a readable claim — this contract would take 500 USDC and grant an unlimited approval — so an obviously wrong outcome can be refused at the confirmation screen rather than discovered afterwards. Simulation is not a guarantee: state can change between the preview and inclusion, and a contract can behave differently depending on who calls it.