System Design Jan 12, 2026 | 6 min read

Designing APIs for Scale

Stable APIs are less about clever endpoints and more about contracts, versioning discipline, and observability.

Start with contract boundaries

Before implementation, define a contract that can survive product changes. Keep request and response shapes explicit and avoid leaking database models into the API layer.

Design for additive change

Most growth issues come from breaking existing clients. Favor additive fields, deprecate slowly, and use versioning only when behavior must change significantly.

Operational patterns that matter

  • Publish a clear error schema with actionable codes.
  • Include request IDs for traceability across logs and clients.
  • Set strict latency budgets for critical endpoints and measure them continuously.

Final note

When API contracts are treated as product interfaces, teams ship faster because downstream consumers trust integration stability.