To support ERC-4337, wallets must implement a smart contract that is required to have two functions:

• validateUserOp, which takes a UserOperation as input. This function is supposed to verify the signature and nonce on the UserOperation, pay the fee and increment the nonce if verification succeeds, and throw an exception if verification fails.
• An op execution function, that interprets calldata as an instruction for the wallet to take actions. How this function interprets the calldata and what it does consequently is completely open-ended. However, we expect the most common behavior would be to parse the calldata as an instruction for the wallet to make one or more calls.

The ERC-4337 core team has implemented SimpleAccount.sol (opens in a new tab), a sample minimal account that extends BaseAccount.sol (opens in a new tab), which implements the IAccount (opens in a new tab) interface.