User Operation

In the context of Account Abstraction via ERC-4337, a User Operation is a pseudo-transaction object. Unlike a traditional blockchain transaction, which is signed by an Externally Owned Account (EOA), a User Operation is a package of data that describes a desired action—such as a token transfer or a smart contract interaction—to be executed by a smart contract wallet. This structure is submitted to a dedicated mempool, where Bundlers (special network participants) collect, validate, and package them into a single on-chain transaction for execution.

The core components of a User Operation include the sender (the smart account address), the nonce, the callData (the encoded target and function calls), the signature, and critical fields for the paymaster and bundler ecosystem like maxFeePerGas and maxPriorityFeePerGas. Crucially, it also contains a paymasterAndData field, which enables gas sponsorship and payment in ERC-20 tokens, and a signature that can be validated by custom logic within the smart account, enabling features like social recovery and multisig approvals.

This abstraction decouples transaction execution from its payment and validation. A Bundler pays the gas fees to include the operation on-chain and is reimbursed by either the sender's smart account or a Paymaster. This model enables key user experience improvements impossible with EOAs, including: - Gasless transactions (sponsored by dApps) - Session keys for automated actions - Atomic multi-operations (batch calls) - Flexible signature schemes (e.g., biometrics).

The lifecycle of a User Operation begins when a client (like a wallet) constructs and signs it, then broadcasts it to a peer-to-peer mempool. Bundlers simulate the operation's validity using the eth_call RPC method against a EntryPoint contract to ensure it will pay fees, then bundle it for on-chain execution. The EntryPoint contract acts as a singleton, orchestrating the final atomic execution, fee payment, and reimbursement, ensuring the system's security and consistency.

User Operations are foundational to achieving account abstraction without requiring consensus-layer changes to Ethereum. By standardizing intent representation, ERC-4337 and User Operations create a permissionless ecosystem for smart account innovation, allowing wallet developers to build more secure and user-friendly experiences while maintaining compatibility with Ethereum's existing infrastructure and security model.

A User Operation is a pseudo-transaction object defined by ERC-4337 that describes an action a smart contract wallet, or account, wants to perform. Unlike a traditional blockchain transaction sent directly to a mempool, a User Operation is broadcast to a peer-to-peer network where specialized nodes called Bundlers collect and submit them. The core structure includes fields for the target contract, call data, signatures, and crucially, parameters for gas payment and validation, decoupling the transaction's execution from its sponsorship.

The lifecycle begins when a user's wallet client creates and signs a User Operation. It is then sent to a network of Bundlers via a dedicated UserOperation mempool. Bundlers perform an initial simulation, called eth_estimateUserOperationGas, to verify the operation will pass on-chain validation. This simulation checks the account's signature and pays a preliminary fee, preventing spam. A Bundler that selects the operation will then package, or bundle, it into a single transaction sent to a special EntryPoint contract on the blockchain.

Upon receiving the bundle, the EntryPoint contract acts as a central orchestrator. It first calls the validateUserOp function on the user's smart account to verify the signature and pay any upfront gas. If validation passes, the EntryPoint executes the account's logic via execute. A key innovation is the paymaster model, where a third-party contract can sponsor gas fees, allowing for meta-transactions. Finally, the EntryPoint reimburses the Bundler and any paymaster, ensuring all parties are compensated for their work, completing the abstracted transaction flow.

A User Operation is a standardized, pseudo-transaction object defined by ERC-4337 that encapsulates a user's intent for execution by a decentralized network of bundlers. Unlike a traditional transaction signed by an Externally Owned Account (EOA), a User Operation is signed by a smart contract wallet (or Account Abstraction wallet). Its core fields include the sender's address (sender), the target contract (to), calldata (data), a signature (signature), and critical parameters for gas management and paymaster sponsorship. This structure enables advanced features like gas abstraction, session keys, and batched operations.

The technical fields of a User Operation are meticulously designed for verification and execution by the EntryPoint contract. Key fields include nonce for replay protection, initCode for wallet deployment, callData for the desired actions, callGasLimit, verificationGasLimit, and preVerificationGas. The paymasterAndData field allows a paymaster to sponsor transaction fees. A bundler collects these operations, validates them against the EntryPoint, and submits them as a single bundled transaction to the underlying blockchain, abstracting gas complexities from the end-user.

This abstraction enables sophisticated transaction flows. For example, a User Operation can specify multiple calls (to and callData) to be executed atomically, sponsor gas fees via a paymaster in a stablecoin, or include signature logic for social recovery. The separation of verification (handled by the smart wallet) and execution (handled by the EntryPoint) is central to its design, allowing for arbitrary signature schemes and security models without requiring changes to the core Ethereum protocol.