NFT Allowlist and Presale Mechanics

Question 1

What data structure is most commonly used to implement gas-efficient NFT allowlists on Ethereum?

Accepted Answer

Merkle tree

Answer

Linked list of addresses

Answer

Binary search tree

Answer

On-chain address array

Question 2

In a Merkle tree allowlist, what must a user provide at mint time to prove they are on the list?

Accepted Answer

A Merkle proof consisting of sibling hashes along the tree path

Answer

Their wallet's private key signature

Answer

The full array of all allowlisted addresses

Answer

A signed transaction from the contract owner

Question 3

Which OpenZeppelin library provides Merkle proof verification for NFT allowlists?

Accepted Answer

@openzeppelin/contracts/utils/cryptography/MerkleProof.sol

Answer

@openzeppelin/contracts/utils/Arrays.sol

Answer

@openzeppelin/contracts/security/ReentrancyGuard.sol

Answer

@openzeppelin/contracts/token/ERC721/ERC721.sol

Question 4

What is the primary gas advantage of Merkle tree allowlists over storing all allowed addresses in an on-chain mapping?

Accepted Answer

Only the 32-byte root is stored on-chain, regardless of how many addresses are allowlisted

Answer

Merkle proofs are computed in fewer EVM opcodes

Answer

Mappings require more function calls to initialize

Answer

Merkle trees compress addresses to 16 bytes each

Question 5

How is a Merkle leaf typically generated from an Ethereum address in Solidity for allowlist verification?

Accepted Answer

keccak256(abi.encodePacked(address))

Answer

abi.encode(address)

Answer

sha256(abi.encode(address))

Answer

bytes32(uint256(uint160(address)))

Question 6

What does the Merkle root stored in an NFT smart contract cryptographically represent?

Accepted Answer

A commitment to the entire set of allowlisted addresses that changes if any address changes

Answer

The hash of the first token minted from the contract

Answer

The IPFS CID of the collection's metadata folder

Answer

The contract deployer's address encoded as bytes32

Question 7

How does verification gas cost scale as the allowlist size grows in a Merkle tree implementation?

Accepted Answer

O(log n) — logarithmically with list size, because proof length equals tree depth

Answer

O(1) — constant, regardless of list size

Answer

O(n) — linearly with list size

Answer

O(n²) — quadratically due to sibling hash comparisons