1. UserOp

A UserOp is not a transaction.

It’s a struct containing fields like:

• sender – your smart account
• nonce
• initCode – lets your account deploy itself automatically
• callData – what you want the account to execute
• callGasLimit
• verificationGasLimit
• paymasterAndData – the gas sponsor logic
• signature

Why this design?

Because simulations must be trustless.

UserOps cannot read dynamic chain data (block timestamp, blockhash, etc.).

That prevents simulation mismatch attacks.

UserOp Mempool

The mempool has rules: