Interview struggle: ERC-20 & ERC-721 questions Need Advice!

ERC-20 and ERC-721 standards are super important for smart contract development on Ethereum. To put it simply, ERC-20 is all about fungible tokens, which means they’re interchangeable and have the same value. You can think of them as cryptocurrencies or in-game currencies.

On the other side, ERC-721 is for non-fungible tokens (NFTs), which are unique and can’t be swapped on a one-to-one basis perfect for digital art or collectibles.

If you’re building a decentralized application (dApp) that includes both types of tokens, you’ll need to work with these standards in your smart contracts. For fungible tokens, using ERC-20 will make sure your tokens are compatible with wallets and exchanges, so users can easily transfer and trade them. You’ll want to implement basic functions like transfer, approve, and transfer for smooth interactions.

When it comes to NFTs, ERC-721 enables the creation of one-of-a-kind digital assets. I It implements functions like mint, transferFrom, and ownerOf to manage these unique items. By sticking to these standards, it ensures that dApp is user-friendly and fits well into the wider Ethereum ecosystem, setting you up for success!

Hey fam,
Totally get the anxiety around ERC-20 & ERC-721 interview questions. Most interviews skip the Wikipedia stuff. They want to see if you’ve actually built and fought fires with these tokens.

For ERC-20, don’t just rattle off functions. Real devs know where things break. For example, talk about decimals mismatches. You’d be surprised how many projects mess this up, causing chaos in integrations or bridges. And don’t ignore the classic allowance race condition with approve/transferFrom; mentioning the two-step update (set to zero, then set the new value) or using increaseAllowance will show you’ve seen real exploits. Bonus: bring up gas optimizations like minimizing state writes.

For ERC-721? Study about Go past transfers. Know why safeTransferFrom is a must for contracts, and how bad things get if a token is sent to a dumb contract via transferFrom. Nerd out a bit on on-chain SVGs or batch transfer limitations (hint: compare to ERC-1155). Also, approvals are a minefield for phishing—show you’re on top of security.

Pro tip: You should be ready with your questions to ask to the recruiter so showcase your curiosity/ You can ask about their race condition handling or how they store NFT metadata at scale. This will shows you’re not just applying, you’re a curios mind and informed decision maker.

Good luck, and remember—it’s the war stories and real-life edge cases that get you the offer, not the textbook answers! 

You can expect the interview question that asks about these ERC-721 extensions, here’s what you should highlight:

Explain it in real-world terms:

Say: “Including the Metadata extension is essential because it stores the name, image, and details for every NFT. Without it, platforms like OpenSea can’t show what your NFT actually is—so your tokens might just look like blank boxes to users. No one wants invisible NFTs!”

Try to give a strong analogy:

“It’s kind of like sending someone a baseball card in a plain envelope with no picture or stats. The collectors can’t appreciate the card if they can’t see anything about it!”

Highlight why Enumerable matters:

“Enumerable is what allows anyone (including marketplaces and wallet apps) to pull a list of all NFTs someone owns, or all NFTs in a collection. Without it, there’s no easy ‘Browse all’ or ‘My NFTs’ functionality. It makes life harder for users and hurts your NFT’s visibility.”

What the interviewer is really looking for:

Mention: “If your NFT is missing either Metadata or Enumerable, getting listed and displayed properly on mainstream marketplaces becomes a serious challenge. Users may not see images or even find all their tokens. It’s a dealbreaker for collectors and projects aiming for broad adoption.”

Pro tip to stand out:

Add: “I’d always include both from the start—even if it takes a little extra effort—because it sets the project up for success later. Cutting corners here will create headaches and likely force you to patch things later, which is way more work than just doing it right upfront.”

Bonus—show you care about user experience:

“I’m always thinking about the end user’s journey. These extensions might seem ‘optional’ but they’re really not if you want your NFTs to be accessible, discoverable, and collectible on the platforms that matter.”

Direct, confident, and focused on practical impact—answering this way shows you know the tech and care about real-world results.

Read more threads to understand about ERC tokens and NFTS https://artofblockchain.club/article/blockchain-gaming-developer-play-to-earn-and-gamefi-careers-the-ultimate-2025-roadmap

https://artofblockchain.club/article/the-ultimate-guide-to-nft-careers-in-2025-high-paying-jobs-beyond-art

https://artofblockchain.club/discussion/how-to-ensure-compatibility-between-erc-721-and-erc-1155-nft-standards