Five API Design Mistakes to Avoid

Poorly considered API decisions can compound and become expensive to change as more clients and systems depend on them.

Common API design issues to look for include:

**1. Versioning too late** You launch v1. Six months later you need breaking changes. Now you're maintaining v1 and v2 forever. Instead, assume you'll need v2. Design for it from day one.

**2. Inconsistent response shapes** Users get inconsistent, items get an array, pagination is sometimes missing. Frontend code becomes defensive. Defensive code is fragile and buggy. Consistency is a feature.

**3. Timestamps without timezones** "2026-04-16 14:30:00" — in what timezone? Always use ISO 8601 with timezone: "2026-04-16T14:30:00Z"

**4. Pagination without sort order** You return 100 items, but not deterministically. Second request might return different items. Your frontend can't build reliable infinite scroll. Always specify sort order.

**5. Assuming status codes are enough** HTTP 400 tells you nothing. "Invalid email" or "Username taken"? Add a specific error code. Make developer lives better.

**The pattern:** Good API design thinks about the developer using it, not just the data flowing through it. Small choices compound into either a joy or a nightmare.

Get these right and your API is still usable years later. Get them wrong and you're rebuilding it every 18 months.