Sponsor gas with Pimlico

Send a transaction from an ERC-4337 smart account on Sei Testnet while a Pimlico paymaster pays the gas, with permissionless.js and viem.

With gas sponsorship, your users do not need SEI to use your dApp. A paymaster pays the gas instead. This recipe uses Pimlico’s bundler and paymaster on Sei Testnet. It creates an ERC-4337 smart account and sends its first transaction without any SEI in the account.

How it works

An ERC-4337 smart account is a contract wallet. It sends a user operation instead of a normal transaction:

1. Your code builds a user operation and signs it with the owner key of the smart account.
2. Pimlico’s paymaster agrees to pay for the operation.
3. Pimlico’s bundler submits the operation to the EntryPoint contract on Sei.
4. The first operation also deploys the smart account contract.

Before you start

• A Pimlico API key. Create one in the Pimlico dashboard.
• Node.js 18 or later.

Put the API key and an owner key in environment variables. The owner key can be any new private key, such as one from generatePrivateKey() in viem/accounts. The account does not need SEI:

export PIMLICO_API_KEY=pim_xxxxxxxxxxxxxxxxxxxxxx
export PRIVATE_KEY=0xYourPrivateKey

Install

npm install viem permissionless

If npm stops with an ERESOLVE error about the ox package, run npm install viem permissionless --legacy-peer-deps. permissionless.js declares an optional peer version of ox that can differ from the version that viem installs.

Send a sponsored transaction

sponsored.mts

import { createPublicClient, http } from 'viem';
import { privateKeyToAccount } from 'viem/accounts';
import { seiTestnet } from 'viem/chains';
import { createSmartAccountClient } from 'permissionless';
import { toSimpleSmartAccount } from 'permissionless/accounts';
import { createPimlicoClient } from 'permissionless/clients/pimlico';

const pimlicoUrl = `https://api.pimlico.io/v2/${seiTestnet.id}/rpc?apikey=${process.env.PIMLICO_API_KEY}`;

const publicClient = createPublicClient({ chain: seiTestnet, transport: http() });
const pimlicoClient = createPimlicoClient({ chain: seiTestnet, transport: http(pimlicoUrl) });

// A smart account that a single private key controls
const account = await toSimpleSmartAccount({
  client: publicClient,
  owner: privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`),
});
console.log('Smart account:', account.address);

const smartAccountClient = createSmartAccountClient({
  account,
  chain: seiTestnet,
  bundlerTransport: http(pimlicoUrl),
  paymaster: pimlicoClient,
  userOperation: {
    estimateFeesPerGas: async () => (await pimlicoClient.getUserOperationGasPrice()).fast,
  },
});

const hash = await smartAccountClient.sendTransaction({
  to: '0xd8da6bf26964af9d7eed9e03e53415d37aa96045',
  value: 0n,
  data: '0x1234',
});
console.log('Transaction hash:', hash);

Run it with npx tsx sponsored.mts. Keep the .mts extension. The script uses top-level await, which works only when Node.js loads the file as an ES module.

You are done when you see:

Smart account: 0x3308a63562c135E899E0D03F82dcbC081E40aA50
Transaction hash: 0x61d675675af6dc6e17fa05463f3e7d81c9710d506689eef425cbc180abf346bf

The smart account address depends on the owner key, so yours differs. The account holds no SEI, but the transaction still succeeds because the paymaster paid for it. sendTransaction returns after the operation is included in a block. To see the transaction that the bundler submitted, look up the hash on Seiscan.

Notes

• EntryPoint version. toSimpleSmartAccount uses EntryPoint v0.7 at 0x0000000071727De22E5E9d8BAf0edAc6f37da032 by default. EntryPoint v0.6, v0.7, and v0.8 are deployed on Sei Testnet.
• Other account types. permissionless.js also supports Safe, Kernel, and other smart accounts. See Pimlico’s smart account comparison.
• Cost. Pimlico sponsors testnet operations for free. On Sei Mainnet, Pimlico bills you for the gas that its paymaster pays, so you need a paid plan. See Pimlico pricing. To use Sei Mainnet, replace seiTestnet with sei.
• Spending limits. Sponsorship policies in the Pimlico dashboard limit how much you sponsor per transaction, per user, or in total.

Related recipes

• Send SEI: send a normal transaction from a funded account
• Pimlico integration: the full walkthrough, with a step-by-step explanation of each client