# TxEnvelopeEip1559.assert

Asserts a [`TxEnvelopeEip1559.TxEnvelopeEip1559`](/api/TxEnvelopeEip1559/types#txenvelopeeip1559) is valid.

## Imports

:::code-group
```ts [Named]
import { TxEnvelopeEip1559 } from 'ox'
```

```ts [Entrypoint]
import * as TxEnvelopeEip1559 from 'ox/TxEnvelopeEip1559'
```
:::

## Examples

```ts twoslash
import { TxEnvelopeEip1559, Value } from 'ox'

TxEnvelopeEip1559.assert({
  maxFeePerGas: 2n ** 256n - 1n + 1n,
  chainId: 1,
  to: '0x0000000000000000000000000000000000000000',
  value: Value.fromEther('1')
})
// @error: FeeCapTooHighError:
// @error: The fee cap (`masFeePerGas` = 115792089237316195423570985008687907853269984665640564039457584007913 gwei) cannot be
// @error: higher than the maximum allowed value (2^256-1).
```

## Definition

```ts
function assert(
  envelope: PartialBy<TxEnvelopeEip1559, 'type'>,
): void
```

**Source:** [src/core/TxEnvelopeEip1559.ts](https://github.com/wevm/ox/blob/main/src/core/TxEnvelopeEip1559.ts#L654)

## Parameters

### envelope

* **Type:** `PartialBy<TxEnvelopeEip1559, 'type'>`

The transaction envelope to assert.

## Return Type

`void`