📦 Prepare Claim List

This page explains how to prepare the eligible wallets list for a Dropsy airdrop, also known as the Claim List, and generate the Merkle tree root, which is required to create an on-chain airdrop.

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Purpose

The Claim List is a structured list of wallets and their eligible token amounts for an airdrop.
Using this list, we generate a Merkle tree, which allows:

• Efficient verification of claims on-chain.
• Preventing users from claiming more than their allocated amount.
• Minimal storage footprint on Solana.

The Merkle root derived from this list is a required argument when creating a new airdrop.

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Step 1: Install dependencies

We use merkletreejs for generating the Merkle tree and Node’s crypto module for hashing.

npm install merkletreejs

crypto comes built-in with Node.js, no need to install separately.

Step 2: Create a utility file

Create a new file /utils/merkle.ts to define helpers for building the Merkle tree.

import { createHash } from "crypto";
import MerkleTree from "merkletreejs";

/**
 * Hash a single claim entry (leaf) with SHA256.
 */
export function hashLeaf(
  index: number,
  address: string,
  amount: number
): Buffer {
  const data = `${index}:${address}:${amount.toString()}`;
  return createHash("sha256").update(data).digest();
}

/**
 * Generate a ReadonlyUint8Array from a Merkle tree root.
 * This is the format expected by the on-chain program.
 */
export const getMerkleRootArray = (
  merkleTree: MerkleTree
): ReadonlyUint8Array => {
  const root = merkleTree.getRoot();

  if (root.length !== 32) {
    throw new Error("Merkle root must be 32 bytes");
  }

  // Convert Buffer → Uint8Array
  return new Uint8Array(root) as ReadonlyUint8Array;
};

/**
 * Create a Merkle tree from a claim list.
 * Each entry must include: index, wallet address, and amount.
 */
export const createMerkleTree = (
  claimList: { index: number; address: string; amount: number }[]
) => {
  const leaves = claimList.map(({ index, address, amount }) =>
    hashLeaf(index, address, amount)
  );

  return new MerkleTree(
    leaves,
    (data: Buffer) => createHash("sha256").update(data).digest(),
    { sortPairs: true }
  );
};

Step 3: Usage example

import { createMerkleTree, getMerkleRootArray } from "./utils/merkle"; // verify path
const claimList = [
  { index: 0, address: "WalletAddress1", amount: 100 },
  { index: 1, address: "WalletAddress2", amount: 200 },
  // Add more eligible wallets here
];

// 1️⃣ Create Merkle tree
const merkleTree = createMerkleTree(claimList);

// 2️⃣ Get Merkle root in the format expected by the program
const merkleRoot = getMerkleRootArray(merkleTree);

console.log("Merkle Root:", merkleRoot);

note

The merkleRoot can now be passed as an argument when creating a new airdrop on-chain.

✅ Summary

• Prepare Claim List → Wallets & amounts

• Generate Merkle Tree → Derive Merkle root