> ## Documentation Index
> Fetch the complete documentation index at: https://voltaire.tevm.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# ERC-4337 Account Abstraction

> Build and send UserOperations for smart contract wallets

<Warning>
  **Looking for Contributors!** This Skill needs an implementation.

  Contributing a Skill involves:

  1. Writing a reference implementation with full functionality
  2. Adding comprehensive tests
  3. Writing documentation with usage examples

  See the [ethers-provider Skill](https://github.com/evmts/voltaire/tree/main/examples/ethers-provider) for an example of a complete Skill implementation.

  Interested? Open an issue or PR at [github.com/evmts/voltaire](https://github.com/evmts/voltaire).
</Warning>

<Info>
  **Skill** — Copyable reference implementation. Use as-is or customize. See [Skills Philosophy](/concepts/skills).
</Info>

Build, sign, and send ERC-4337 UserOperations for smart contract wallets. Interact with bundlers and paymasters.

## Why Account Abstraction?

Traditional EOA wallets have limitations:

* Single key = single point of failure
* Can't batch transactions
* User pays gas in ETH only
* No account recovery

Smart contract wallets (ERC-4337) enable:

* Multi-sig, social recovery
* Batch transactions
* Sponsored gas (paymasters)
* Session keys, spending limits
* Any token for gas

## Planned Implementation

### Build UserOperation

```typescript theme={null}
import { UserOperation } from './UserOperation.js';

const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  // Optional: use paymaster for sponsored gas
  paymaster: PAYMASTER_ADDRESS,
  // Signer for the smart wallet
  signer,
  // EntryPoint version
  entryPoint: ENTRYPOINT_V07,
});

// userOp is ready to send to bundler
```

### Send to Bundler

```typescript theme={null}
import { Bundler } from './Bundler.js';

const bundler = Bundler('https://api.pimlico.io/v2/1/rpc?apikey=...');

// Send UserOperation
const userOpHash = await bundler.sendUserOperation(userOp);

// Wait for inclusion
const receipt = await bundler.waitForUserOperation(userOpHash);
console.log('Included in tx:', receipt.transactionHash);
```

### Batch Transactions

```typescript theme={null}
// Execute multiple calls in one UserOperation
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  calls: [
    { to: USDC, data: encodeApprove(spender, amount) },
    { to: DEX, data: encodeSwap(USDC, WETH, amount) },
    { to: WETH, data: encodeWithdraw() },
  ],
  signer,
});
```

### Paymaster (Sponsored Gas)

```typescript theme={null}
// User pays no gas - paymaster covers it
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  paymaster: {
    address: PAYMASTER_ADDRESS,
    // Get paymaster signature
    getData: async (partialUserOp) => {
      return await paymasterService.sign(partialUserOp);
    }
  },
  signer,
});
```

### ERC-20 Gas Payment

```typescript theme={null}
// Pay gas in USDC instead of ETH
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(recipient, amount),
  paymaster: {
    address: TOKEN_PAYMASTER,
    token: USDC_ADDRESS,
    // Paymaster will pull USDC from user for gas
  },
  signer,
});
```

### Session Keys

```typescript theme={null}
// Create limited session key
const sessionKey = await SessionKey.create({
  wallet: smartWalletAddress,
  permissions: {
    // Only allow transfers to specific addresses
    allowedTargets: [FRIEND_ADDRESS],
    // Max 100 USDC per transaction
    maxAmount: parseUnits('100', 6),
    // Valid for 24 hours
    validUntil: Date.now() + 86400000,
  },
  mainSigner,
});

// Use session key (no main key needed)
const userOp = await UserOperation.build({
  sender: smartWalletAddress,
  callData: encodeTransfer(FRIEND_ADDRESS, parseUnits('50', 6)),
  signer: sessionKey,
});
```

## Bundler Providers

Popular bundler services:

* [Pimlico](https://pimlico.io)
* [Alchemy](https://alchemy.com)
* [Stackup](https://stackup.sh)
* [Biconomy](https://biconomy.io)

```typescript theme={null}
// Pimlico
const bundler = Bundler('https://api.pimlico.io/v2/1/rpc?apikey=KEY');

// Alchemy
const bundler = Bundler('https://eth-mainnet.g.alchemy.com/v2/KEY');

// Self-hosted
const bundler = Bundler('http://localhost:3000/rpc');
```

## Smart Wallet Factories

Support for popular smart wallet implementations:

```typescript theme={null}
// Safe (Gnosis)
import { SafeAccount } from './accounts/safe.js';

// Kernel (ZeroDev)
import { KernelAccount } from './accounts/kernel.js';

// SimpleAccount (reference impl)
import { SimpleAccount } from './accounts/simple.js';
```

## Resources

* [ERC-4337 Specification](https://eips.ethereum.org/EIPS/eip-4337)
* [eth-infinitism/account-abstraction](https://github.com/eth-infinitism/account-abstraction)
* [ERC-4337 Bundler Spec](https://github.com/eth-infinitism/bundler-spec)

## Related

* [ethers-signer](/skills/ethers-signer) — EOA signing
* [permit](/skills/permit) — Gasless approvals
* [multicall](/skills/multicall) — Batch reads