> ## 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.

# BlockHash

> 32-byte block identifier

## Overview

BlockHash is a branded `Uint8Array` type representing a 32-byte block identifier in Ethereum. Every block has a unique hash computed from its header.

```typescript theme={null}
import * as BlockHash from '@tevm/primitives/BlockHash'

const hash = BlockHash.fromHex(
  '0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890'
)
```

## Type Definition

```typescript theme={null}
type BlockHashType = Uint8Array & {
  readonly [brand]: "BlockHash";
  readonly length: 32;
}
```

## Creating BlockHashes

### from

Universal constructor accepting hex string or bytes.

```typescript theme={null}
// From hex string
const hash1 = BlockHash.from(
  '0xabcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890'
)

// From bytes
const bytes = new Uint8Array(32)
const hash2 = BlockHash.from(bytes)
```

### fromHex

Parse from hex string (with or without 0x prefix).

```typescript theme={null}
const hash = BlockHash.fromHex(
  'abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890'
)
```

**Validation**: Must be 64 hex characters (32 bytes).

### fromBytes

Create from `Uint8Array`.

```typescript theme={null}
const bytes = new Uint8Array(32)
const hash = BlockHash.fromBytes(bytes)
```

**Validation**: Must be exactly 32 bytes.

## Converting BlockHashes

### toHex

Convert to lowercase hex string with 0x prefix.

```typescript theme={null}
const hex = BlockHash.toHex(hash)
// '0xabcdef1234567890...'
```

## Comparing BlockHashes

### equals

Check equality using constant-time byte comparison.

```typescript theme={null}
const a = BlockHash.fromHex('0xabcd...')
const b = BlockHash.fromHex('0xabcd...')

if (BlockHash.equals(a, b)) {
  console.log('Hashes are equal')
}
```

## Errors

**InvalidBlockHashLengthError**: Bytes length is not 32.

**InvalidBlockHashFormatError**: Invalid hex format or unsupported type.

## See Also

* [BlockHash (Effect)](https://voltaire-effect.tevm.sh/primitives/block-hash) - Effect.ts integration with Schema validation
* [BlockNumber](/primitives/block-number) - Block height
* [TransactionHash](/primitives/transaction-hash) - Transaction identifier
* [Receipt](/primitives/receipt) - Transaction receipts