# Operations

* **`UserOperation`:** 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 `UserOperation` 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.
* **`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.
* **`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.  
* **`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.

***

The lifecycle of transition looks like this:

<figure><img src="https://2952380122-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FuD7AmV6zHVSdf9W2Sjm4%2Fuploads%2FPWgaSiOemetV2kCNMhlu%2F4337%20Submit%20UserOperation%20to%20bundler.08324fee.svg?alt=media&#x26;token=443f8e6f-7ebb-4357-bad3-16b5a93beb56" alt=""><figcaption><p><a href="https://www.erc4337.io/docs/understanding-ERC-4337/architecture">Source</a></p></figcaption></figure>

## UserOperation

`UserOperation` 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 `UserOperation` so dapps' frontends don't need to change anything to support ERC-4337.

<table data-full-width="false"><thead><tr><th width="276">Field</th><th width="141">Type</th><th>Description</th></tr></thead><tbody><tr><td><code>sender</code></td><td><code>address</code></td><td>The address of the smart contract account</td></tr><tr><td><code>nonce</code></td><td><code>uint256</code></td><td>Anti-replay protection; also used as the salt for first-time account creation</td></tr><tr><td><code>initCode</code></td><td><code>bytes</code></td><td>Code used to deploy the account if not yet on-chain</td></tr><tr><td><code>callData</code></td><td><code>bytes</code></td><td>Data that's passed to the sender for execution</td></tr><tr><td><code>callGasLimit</code></td><td><code>uint256</code></td><td>Gas limit for execution phase</td></tr><tr><td><code>verificationGasLimit</code></td><td><code>uint256</code></td><td>Gas limit for verification phase</td></tr><tr><td><code>preVerificationGas</code></td><td><code>uint256</code></td><td>Gas to compensate the bundler</td></tr><tr><td><code>maxFeePerGas</code></td><td><code>uint256</code></td><td>Maximum fee per gas (similar to <a href="https://eips.ethereum.org/EIPS/eip-1559">EIP-1559(opens in a new tab)</a> <code>max_fee_per_gas</code>)</td></tr><tr><td><code>maxPriorityFeePerGas</code></td><td><code>uint256</code></td><td>Maximum priority fee per gas (similar to EIP-1559 <code>max_priority_fee_per_gas</code>)</td></tr><tr><td><code>paymasterAndData</code></td><td><code>bytes</code></td><td>Paymaster Contract address and any extra data required for verification and execution (empty for self-sponsored transaction)</td></tr><tr><td><code>signature</code></td><td><code>bytes</code></td><td>Used to validate a UserOperation along with the nonce during verification</td></tr></tbody></table>


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