Design NFT Marketplace - System Design | WinJob

Problem Statement: NFT Marketplace at OpenSea Scale

Design an OpenSea-class NFT marketplace where collectors connect wallets, creators mint collections, and trades settle on-chain via signed off-chain orders. This section covers problem statement: nft marketplace at opensea scale during the understanding phase.

Mechanism

primary flows: connect wallet, mint collection, list fixed-price or auction, settle on-chain
off-chain order book with on-chain settlement via Seaport-style matchers
metadata on IPFS/Arweave with CDN preview and integrity checks

Invariants and consistency

Treat ownership rows as CP (strong per token_id) while gallery/search tiles may lag 5–15s behind chain head under load. Orders are off-chain intent until a mined transaction proves fulfillment—never mark sold without tx receipt + log index.

Failure modes

duplicate mint from replayed signatures
stale ownership shown after transfer outside marketplace
gas spike during hyped drops freezing checkout UX

Interview checkpoint (sec-01-understanding-1)

State numeric assumptions before SKUs: peak search RPS, order write RPS, indexer lag p95, and reorg depth. Tie each component to a metric an OpenSea/Rarible interviewer can probe.

javaOne Dark Pro

1 public record TokenId(String contract, BigInteger tokenId) {}

pythonOne Dark Pro

1 def pack_token_id(contract: str, tid: int) -> str:
2     return f"{contract.lower()}:{tid}"

typescriptOne Dark Pro

1 export function tokenKey(contract: string, tokenId: bigint): string {
2   return `${contract.toLowerCase()}:${tokenId}`;
3 }

Why interviewers care

NFT Marketplace interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.

Interview checkpoint

Name one failure story for Problem Statement: NFT Marketplace at OpenSea Scale that proves you understand real outages, not happy-path diagrams.

Key Highlights

•primary flows: connect wallet, mint collection, list fixed-price or auction, settle on-chain
•off-chain order book with on-chain settlement via Seaport-style matchers
•metadata on IPFS/Arweave with CDN preview and integrity checks

1	def pack_token_id(contract: str, tid: int) -> str:
2	return f"{contract.lower()}:{tid}"

1	export function tokenKey(contract: string, tokenId: bigint): string {
2	return `${contract.toLowerCase()}:${tokenId}`;
3	}