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# `l2.buildProveWithdrawal`

Builds the output root and storage proof required to prove an [L2 withdrawal](/op-stack/withdrawals) on L1.

## Usage

Build a proof from a legacy L2 output proposal and an extracted withdrawal.

:::code-group
```ts twoslash [example.ts]
import type { Actions, Withdrawal } from 'viem/op-stack'
import { client } from './viem.config'

declare const output: Actions.l2.buildProveWithdrawal.Output
declare const withdrawal: Withdrawal.Withdrawal

const proof = await client.withdrawal.buildProveWithdrawal({ // [!code focus:4]
  output,
  withdrawal,
})
// @log: { l2OutputIndex: 42n, outputRootProof: { ... }, withdrawalProof: ['0x...'], ... }
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/op-stack/l2.config.ts:setup]
```
:::

### Standalone Action

Call `Actions.l2.buildProveWithdrawal` directly by passing the Client as the first argument.

:::code-group
```ts twoslash [example.ts]
import { Actions, type Withdrawal } from 'viem/op-stack'
import { client } from './viem.config'

declare const output: Actions.l2.buildProveWithdrawal.Output
declare const withdrawal: Withdrawal.Withdrawal

const proof = await Actions.l2.buildProveWithdrawal(client, { // [!code focus:4]
  output,
  withdrawal,
})
// @log: { l2OutputIndex: 42n, outputRootProof: { ... }, withdrawalProof: ['0x...'], ... }
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/op-stack/l2.config.ts:setup]
```
:::

## Return Value

`Actions.l2.buildProveWithdrawal.ReturnType`

The Account, output index, output root proof, target Chain, withdrawal, and Merkle proof required by the L1 portal.

## Parameters

### account

* **Type:** `Account | Address`
* **Default:** `client.account`

The Account or address that will prove the withdrawal on L1.

### chain

* **Type:** `Chain`
* **Default:** `client.chain`

The L2 Chain containing the withdrawal.

### game

* **Type:** `Actions.l2.buildProveWithdrawal.Game`

The dispute game anchoring the withdrawal. Pass either `game` or `output`.

### output

* **Type:** `Actions.l2.buildProveWithdrawal.Output`

The legacy L2 output proposal anchoring the withdrawal. Pass either `output` or `game`.

### withdrawal

* **Type:** `Withdrawal.Withdrawal`

The withdrawal extracted from the initiating transaction receipt.