OLX / Craigslist — Notes

Functional

• Post / browse classified ads (no integrated checkout).
• Geo + category search.
• In-app chat between buyer & seller.
• Moderation.
• Optional paid promotion.

Non-functional

• Eventual consistency on listings is fine.
• Heavy spam / fraud filtering.
• p99 search < 500 ms.

Capacity

• 100M+ active listings globally for big platforms.
• High image volume; aggressive transcoding.

Schema

• listings(id, owner, category, geo, price, status, body, images[])
• categories(id, parent, attrs[])
• users(id, phone_verified, badges[])
• chats(thread_id, listing_id, [participants])

Trade-offs

• Open marketplace = scam risk; invest in moderation > features.
• No payment integration (classic Craigslist) = simpler but offline fraud risk.
• Chat in-app keeps the conversation auditable for trust & safety.

Refs

• OLX / Mercari / Letgo engineering blogs.
• ByteByteGo "Design a classifieds platform".