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# Blob Transactions

## Overview

EIP-4844 transactions carry temporary blob data outside normal EVM calldata. Viem accepts encoded
blobs and a KZG implementation. Ox provides an opt-in WASM implementation backed by
[`c-kzg-4844`](https://github.com/ethereum/c-kzg-4844).

Viem derives commitments and versioned hashes, signs the transaction, and broadcasts it through
[`transaction.send`](/docs/actions/wallet/transaction/send).

## Recipes

These recipes assume you have [set up a Client](/docs) with a Local Account and installed
[`ox`](https://oxlib.sh) as a direct dependency.

### Encode Blob Data

Use [`Blobs.from`](/docs/utilities/blobs/from) to split arbitrary bytes into correctly encoded blobs.

```ts twoslash
import { Blobs, Hex } from 'viem/utils'

const blobs = Blobs.from(Hex.fromString('Hello from a blob')) // [!code focus]
```

### Configure KZG

Create Ox's WASM KZG implementation with its bundled Ethereum mainnet trusted setup.

```ts twoslash
// @noErrors
import { Setups } from 'ox/trusted-setups'
import { Kzg } from 'ox/wasm'

const kzg = await Kzg.create({ trustedSetup: Setups.mainnet }) // [!code focus]
```

The instance implements Viem's [`Kzg`](/docs/utilities/kzg/from) interface. Call `dispose` when the
application no longer needs the instance.

### Send a Blob Transaction

Pass the blobs and KZG adapter. Viem derives the remaining blob fields during preparation.

:::code-group
```ts twoslash [example.ts]
// @noErrors
import { Setups } from 'ox/trusted-setups'
import { Kzg } from 'ox/wasm'
import { Blobs, Hex } from 'viem/utils'
import { client } from './viem.config'

const kzg = await Kzg.create({ trustedSetup: Setups.mainnet })

try {
  const hash = await client.transaction.send({
    blobs: Blobs.from(Hex.fromString('Hello from a blob')), // [!code focus]
    kzg, // [!code focus]
    to: '0x0000000000000000000000000000000000000000',
  })
} finally {
  kzg.dispose()
}
```

```ts twoslash [viem.config.ts] filename="viem.config.ts"
// [!include ~/snippets/docs/viem.config.ts:setup]
```
:::

## Best Practices

### Reuse and Dispose KZG

Create the WASM instance during process initialization and reuse it across transactions. Call
`dispose` during shutdown to release its c-kzg allocations.

Create one instance inside each JavaScript worker that performs KZG operations.

### Use Blobs for Data Availability

Blob data is temporary and unavailable to EVM execution. Put values required by a contract in
calldata or contract storage instead.

## See More

<Cards>
  <Card icon="lucide:binary" title="Blobs" description="Encode blobs and derive commitments, proofs, or versioned hashes." to="/docs/utilities/blobs" />

  <Card icon="lucide:key-round" title="KZG" description="Configure the commitment interface used by blob transactions." to="/docs/utilities/kzg" />
</Cards>