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

# Merkle Tree Whitelist

> Generate a Merkle tree for whitelist verification and verify proofs on-chain.

# Merkle Tree Whitelist

Generate a Merkle tree for whitelist verification and verify proofs on-chain.

Generate a Merkle tree for whitelist verification and verify proofs on-chain.

## Explanation

Merkle trees allow O(log n) proof verification. The root is stored on-chain; users submit a proof proving their address is in the whitelist. This is far cheaper than storing a mapping of all whitelisted addresses.

## Code

```typescript theme={null}
import { MerkleTree } from "merkletreejs";
import { keccak256, encodePacked, toHex } from "viem";

// Build the tree from whitelist addresses
const whitelist = [
  "0x1234...",
  "0x5678...",
  "0xabcd...",
];

const leaves = whitelist.map((addr) =>
  keccak256(encodePacked(["address"], [addr]))
);

const tree = new MerkleTree(leaves, keccak256, { sortPairs: true });
const root = tree.getHexRoot();

// Generate a proof for a specific address
const leaf = keccak256(encodePacked(["address"], ["0x1234..."]));
const proof = tree.getHexProof(leaf);

console.log("Root:", root);
console.log("Proof:", proof);

// Verify on-chain in your Solidity contract:
// bytes32 leaf = keccak256(abi.encodePacked(msg.sender));
// require(MerkleProof.verify(proof, root, leaf), "Not whitelisted");
```

***

**Canonical knowledge ID:** `code-example:merkle-tree-whitelist`