ERC-4337 UserOp/Bundler/EntryPoint Flow Explained

Wiki route

This entry sits under systems index. Read it against ERC-4337 Overview · Application-Layer Implementation of Account Abstraction for peer / contrast context and fintech index for the broader system / regulatory boundary.

Key facts

• A UserOp is not a transaction; it is a sub-unit packaged by a Bundler ^•
• A Bundler is similar to a block builder, but it operates in the UserOp mempool ^•
• EntryPoint is a singleton contract and the entry point that every UserOp must pass through ^•
• Paymaster is an optional contract that either sponsors gas or accepts gas payment in ERC-20 ^•
• Aggregator is optional and batch-verifies multiple signatures(BLS / others) ^•

Mechanism / How it works

End-to-end flow(typical USDC gas-sponsorship scenario):

1. The user builds a UserOp:the user(or dApp) generates a UserOperation object:

   • sender(SCW address)
   • nonce
   • callData(specific call, e.g., USDC.transfer)
   • callGasLimit / verificationGasLimit / preVerificationGas
   • maxFeePerGas / maxPriorityFeePerGas
   • paymasterAndData(when using a Paymaster)
   • signature(signature of the SCW owner)

2. Send the UserOp to the alt-mempool:the user sends it through the Bundler RPC(eth_sendUserOperation)

3. Bundler simulation + packaging:the Bundler forks state locally and executes the UserOp, confirms that the gas estimate is correct, then packages N UserOps into a standard transaction 1 件 and calls EntryPoint.handleOps()

4. EntryPoint executes:

   • Calls the SCW factory and deploys the SCW(if the SCW does not yet exist)
   • Calls SCW.validateUserOp() to verify the signature + nonce
   • Calls Paymaster.validatePaymasterUserOp() to verify the Paymaster’s sponsorship consent
   • Executes callData(the main business logic)
   • Settles gas:collects from the Paymaster / pays the Bundler

5. On-chain result:the user can confirm the SCW execution result and does not need to hold ETH

Core innovation point:because a UserOp is not a transaction, Bundlers can perform “batch-processing optimization” — packaging 10 件 UserOps into 1 件 transactions and spreading the on-chain base cost.

Origin & evolution

The UserOp structure went through multiple iterations during the 4337 draft period(2021-2022). Early versions had more fields(wallet, separate initCode, etc.), but were later simplified into the current form. The main simplifications from v0.6(2023-03 public version) to v0.7(2026) were:

• Integrating initCode into the sender generation logic
• Splitting Paymaster fields out of calldata and making them explicit
• Reducing gas overhead by 20-30%

The Bundler economic model introduced a priority-fee auction mechanism after v0.7 , mitigating the early problem that “Bundlers are hard to monetize.”

Related

• Wiki Index
• ERC-4337 Overview
• Embedded Wallet Adoption
• ERC-7702

Sources

• ERC-4337 EIP v0.6 / v0.7 spec
• ERC-4337 (Account Abstraction) — https://eips.ethereum.org/EIPS/eip-4337