Understanding ERC-4337


There are several main components to ERC-4337: UserOperation, Bundler, EntryPoint Contract, Account Contract, Account Factory Contract and Paymaster Contract.

  • UserOperations are pseudo-transaction objects that are used to execute transactions with contract accounts. These are created by the dapp. Wallets should be able to translate regular transactions into UserOperations so dapps' frontends don't need to change anything to support ERC-4337
  • Bundlers are actors that package UserOperations from a mempool and send them to the EntryPoint contract on the blockchain. For more detailed documentation on bundlers head on to this part (opens in a new tab) of the documentation.
  • EntryPoint is a smart contract that handles the verification and execution logic for transactions. Account Contracts are smart contract accounts owned by a user.
  • Account Contract is the smart contract wallet of a user. Wallet developers are required to implement at least two custom functions - one to verify signatures, and another to process transactions.
  • Factory Contract - When using a wallet for the first time, the initCode field of the UserOperation is used to specify creation of the smart contract wallet. This is used concurrently with the first actual operation of the wallet (in the same UserOperation). Therefore, wallet developers also need to implement the account factory contract (for example: BLSAccountFactory.sol (opens in a new tab)). Creating new wallets should use the CREATE2 method to ensure the determinacy of generated addresses.
  • Paymaster Contracts are optional smart contract accounts that can sponsor gas fees for Account Contracts, or allow their owners to pay for those fees with ERC-20 tokens instead of ETH. For more detailed documentation on paymasters head on to this part (opens in a new tab) of the documentation.

In practice the process is complex. The typical lifecycle of a transaction looks like this:

Submit UserOperation to bundler flow


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