Send a user operation

User operations are the ERC-4337 counterpart to traditional blockchain transactions. They incorporate significant enhancements that improve user experience and provide greater flexibility in account management and transaction execution.

Viem's Account Abstraction API allows a developer to specify an array of Calls that will be executed as a user operation via Viem's sendUserOperation method. The MetaMask Delegation Toolkit encodes and executes the provided calls.

User operations are not directly sent to the network. Instead, they are sent to a bundler, which validates, optimizes, and aggregates them before network submission. See Viem's Bundler Client for details on how to interact with the bundler.

note

If a user operation is sent from a MetaMask smart account that has not been deployed, the toolkit configures the user operation to automatically deploy the account.

Prerequisites

• Install and set up the Delegation Toolkit.
• Create a MetaMask smart account.

Send a user operation

The following is a simplified example of sending a user operation using Viem Core SDK. Viem Core SDK offers more granular control for developers who require it.

In the example, a user operation is created with the necessary gas limits.

This user operation is passed to a bundler instance, and the EntryPoint address is retrieved from the client.

• example.ts
• config.ts

import { bundlerClient, smartAccount } from "./config.ts";
import { parseEther } from "viem";

// Appropriate fee per gas must be determined for the specific bundler being used.
const maxFeePerGas = 1n;
const maxPriorityFeePerGas = 1n;

const userOperationHash = await bundlerClient.sendUserOperation({
  account: smartAccount,
  calls: [
    {
      to: "0x1234567890123456789012345678901234567890",
      value: parseEther("0.001")
    }
  ],
  maxFeePerGas,
  maxPriorityFeePerGas
});

import { createPublicClient, http } from "viem";
import { createBundlerClient } from "viem/account-abstraction";
import { sepolia as chain } from "viem/chains";
import { generatePrivateKey, privateKeyToAccount } from "viem/accounts";
import { 
  Implementation, 
  toMetaMaskSmartAccount,
} from "@metamask/delegation-toolkit";


const publicClient = createPublicClient({
  chain,
  transport: http()
});

const privateKey = generatePrivateKey(); 
const account = privateKeyToAccount(privateKey);

export const smartAccount = await toMetaMaskSmartAccount({
  client: publicClient,
  implementation: Implementation.Hybrid,
  deployParams: [account.address, [], [], []],
  deploySalt: "0x",
  signer: { account },
});

export const bundlerClient = createBundlerClient({
  client: publicClient,
  transport: http("https://public.pimlico.io/v2/11155111/rpc")
});

Estimate fee per gas

Different bundlers have different ways to estimate maxFeePerGas and maxPriorityFeePerGas, and can reject requests with insufficient values. The following example updates the previous example to estimate the fees.

This example uses constant values, but the Hello Gator example uses Pimlico's Alto bundler, which fetches user operation gas price using the RPC method pimlico_getUserOperationPrice.

Installation required

To estimate the gas fee for Pimlico's bundler, install the permissionless.js SDK.

example.ts

+ import { createPimlicoClient } from "permissionless/clients/pimlico";
import { parseEther } from "viem";
import { bundlerClient, smartAccount } from "./config.ts" // The config.ts is the same as in the previous example.

- const maxFeePerGas = 1n;
- const maxPriorityFeePerGas = 1n;

+ const pimlicoClient = createPimlicoClient({
+   transport: http("https://api.pimlico.io/v2/11155111/rpc"), // You can get the API Key from the Pimlico dashboard.
+ });
+
+ const { fast: fee } = await pimlicoClient.getUserOperationGasPrice();

const userOperationHash = await bundlerClient.sendUserOperation({
  account: smartAccount,
  calls: [
    {
      to: "0x1234567890123456789012345678901234567890",
      value: parseEther("1")
    }
  ],
-  maxFeePerGas,
-  maxPriorityFeePerGas
+  ...fee
});

Wait for the transaction receipt

After submitting the user operation, it's crucial to wait for the receipt to ensure that it has been successfully included in the blockchain. Use the waitForUserOperationReceipt method provided by the bundler client.

example.ts

import { createPimlicoClient } from "permissionless/clients/pimlico";
import { bundlerClient, smartAccount } from "./config.ts" // The config.ts is the same as in the previous example.

const pimlicoClient = createPimlicoClient({
  transport: http("https://api.pimlico.io/v2/11155111/rpc"), // You can get the API Key from the Pimlico dashboard.
});

const { fast: fee } = await pimlicoClient.getUserOperationGasPrice();

const userOperationHash = await bundlerClient.sendUserOperation({
  account: smartAccount,
  calls: [
    {
      to: "0x1234567890123456789012345678901234567890",
      value: parseEther("1")
    }
  ],
  ...fee
});

+ const { receipt } = await bundlerClient.waitForUserOperationReceipt({
+   hash: userOperationHash
+ });
+
+ console.log(receipt.transactionHash);

Next steps

To sponsor gas for end users, see how to send a gasless transaction.