This document proposes a standard interface for ERC-4337 paymasters that require an off-chain service to recieve and approve UserOperations from any source. Background The ERC-4337 standard for account abstraction introduces the concept of a paymaster. This is any entity that is able to sponsor the gas cost of a UserOperation if it meets certain conditions. One interesting use case this enables is the concept of a verifying paymaster. In this case, the on-chain paymaster will sponsor all UserOperations that have been externally signed by a trusted private key. In practice this allows for systems where gas can be abstracted to other forms of off-chain payment methods such as credit card and subscription services. In an ecosystem of smart contract accounts, we could also expect a diversity of paymaster services that any ERC-4337 account can interact with. To promote maximum composibility, we propose all verifying paymasters to expose a standard interface for recieving and sponsoring UserOperations.