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How to create and use a Kernel account with permissionless.js

Kernel is a modular smart account that supports plugins, which are smart contracts that extend the account's functionalities. You can use Kernel with popular plugins such as session keys and account recovery, and even write your own plugins.

Steps

Import the required packages

import { createSmartAccountClient } from "permissionless"
import { signerToEcdsaKernelSmartAccount } from "permissionless/accounts"
import {
	createPimlicoBundlerClient,
	createPimlicoPaymasterClient,
} from "permissionless/clients/pimlico"
import { createPublicClient, getContract, http, parseEther } from "viem"
import { sepolia } from "viem/chains"

Create the clients

First we must create the public, bundler, and (optionally) paymaster clients that will be used to interact with the Kernel account.

export const publicClient = createPublicClient({
	transport: http("https://rpc.ankr.com/eth_sepolia"),
})
 
export const paymasterClient = createPimlicoPaymasterClient({
	transport: http("https://api.pimlico.io/v2/sepolia/rpc?apikey=API_KEY"),
})

Create the signer

Kernel accounts can work with a variety of signing algorithms such as ECDSA, passkeys, and multisig. In permissionless.js, the default Kernel account validates ECDSA signatures. Any signer can be used as a signer for the Kernel account.

For example, to create a signer based on a private key:

import { privateKeyToAccount } from "viem/accounts"
 
const signer = privateKeyToAccount("0xPRIVATE_KEY")

Create the Kernel account

With a signer, you can create a Kernel account as such:

const kernelAccount = await signerToEcdsaKernelSmartAccount(publicClient, {
	entryPoint: "0x5FF137D4b0FDCD49DcA30c7CF57E578a026d2789", // global entrypoint
	signer: signer,
	index: 0n, // optional
	address: "0x...", // optional, only if you are using an already created account
})

The Kernel address is computed deterministically from the signer, but you can optionally pass an index to create any number of different accounts using the same signer. You can also pass an address to use an already created Kernel account.

Create the smart account client

The smart account client is a permissionless.js client that is meant to serve as an almost drop-in replacement for viem's walletClient.

const smartAccountClient = createSmartAccountClient({
	account: kernelAccount,
	chain: sepolia,
	transport: http("https://api.pimlico.io/v1/sepolia/rpc?apikey=API_KEY"),
	sponsorUserOperation: paymasterClient.sponsorUserOperation, // optional
})

Fetch the gas prices (optional)

If you're using Pimlico as your bundler, fetch the required gas price to use beforehand and pass it in as the maxFeePerGas and maxPriorityFeePerGas parameters. Other providers might have different requirements for fetching the gas price.

export const bundlerClient = createPimlicoBundlerClient({
	transport: http("https://api.pimlico.io/v1/sepolia/rpc?apikey=API_KEY"),
})
 
const gasPrices = await bundlerClient.getUserOperationGasPrice()

Send a transaction

Transactions using permissionless.js simply wrap around user operations. This means you can switch to permissionless.js from your existing viem EOA codebase with minimal-to-no changes.

const txHash = await smartAccountClient.sendTransaction({
	to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
	value: parseEther("0.1"),
	maxFeePerGas: gasPrices.fast.maxFeePerGas, // if using Pimlico
	maxPriorityFeePerGas: gasPrices.fast.maxPriorityFeePerGas, // if using Pimlico
})

This also means you can also use viem Contract instances to transact without any modifications.

const nftContract = getContract({
	address: "0xFBA3912Ca04dd458c843e2EE08967fC04f3579c2",
	abi: nftAbi,
	client: {
		public: publicClient,
		wallet: smartAccountClient,
	},
})
 
const txHash = await nftContract.write.mint()

You can also send an array of transactions in a single batch.

const txHash = await smartAccountClient.sendTransactions({
	transactions: [
		{
			to: "0xd8da6bf26964af9d7eed9e03e53415d37aa96045",
			value: parseEther("0.1"),
			data: "0x",
		},
		{
			to: "0x1440ec793aE50fA046B95bFeCa5aF475b6003f9e",
			value: parseEther("0.1"),
			data: "0x1234",
		},
	],
	maxFeePerGas: gasPrices.fast.maxFeePerGas, // if using Pimlico
	maxPriorityFeePerGas: gasPrices.fast.maxPriorityFeePerGas, // if using Pimlico
})