Start with boundaries
The strongest backend systems begin with clear boundaries: auth, billing, notifications, and domain logic should not collapse into one controller layer.
API decisions that scale
- Version public APIs deliberately.
- Use idempotency for critical write operations.
- Separate synchronous responses from async processing.
- Document error contracts early.
Operational readiness
Good API design includes logs, metrics, and incident-friendly error messages. Stability is not just code correctness; it is recovery speed when something fails.