Technical interview guide

Token Standards (ERC-20, ERC-721, ERC-1155)

The interface standards that let wallets, exchanges, and other contracts interact with any token the same way — fungible, non-fungible, and multi-token.

Read: 45 min
Practice MCQs: 25
Interview QA: 25
Edition: v3
Editorial status: Reviewed
Relevant for: Blockchain Developer

Scope: ERC-20, ERC-165, ERC-721, ERC-1155, ERC-2612, ERC-2981, and ERC-4906 specifications; OpenZeppelin Contracts 5.x documentation reviewed 2026-09-04.

Interview QA

Treat each question like a live interview question: answer out loud first (structure, assumptions, tradeoffs), then open the model answer to spot gaps and rehearse a tighter follow-up.

Curated: 2026-10-05 · Written: 2026-10-05 · Reviewed: 2026-10-03

QA-1

Evaluate whether an advertised token is safe to integrate.

QA-2

Handle an ERC-20 allowance change safely.

QA-3

How do ERC-20, ERC-721, and ERC-1155 differ in their storage layout, gas efficiency during batch transfers, and representation of semi-fungible tokens?

QA-4

Minimize approval risk in a dApp.

QA-5

Normalize token and price units in a vault.

QA-6

Integrate ERC-2612 permit into a deposit transaction.

QA-7

Secure mint and burn controls for a backed token.

QA-8

Define which ERC-20 variants a protocol supports.

QA-9

Wrap token movement in invariant-preserving accounting.

QA-10

How does safeTransferFrom protect against stuck tokens in ERC-721, and what reentrancy vectors does it introduce via onERC721Received?

QA-11

How do you implement dynamic, fully on-chain NFT metadata in Solidity, and how does it compare to off-chain storage like IPFS?

QA-12

Implement a secure ERC-721 receiver.

QA-13

Render NFT metadata safely and honestly.

QA-14

Operate a cache for mutable NFT metadata.

QA-15

Choose between enumerable extension and off-chain indexing.

QA-16

Integrate NFT royalties without misleading creators.

QA-17

Model game currencies and unique items with ERC-1155.

QA-18

Implement a gas-bounded multi-token batch transfer.

QA-19

Threat-model an ERC-1155 receiver callback.

QA-20

Build an ERC-1155 balance indexer.

QA-21

Use ERC-165 safely in a marketplace.

QA-22

Design approval UX for a multi-token marketplace.

QA-23

Review privileged powers in a token before listing.

QA-24

Release an upgrade to a widely integrated token.

QA-25