Your API is a product. Integrators do not care how elegant your internal modules are—they care whether endpoints behave the same way on Tuesday as they did on Monday, and whether errors explain what to fix.
Consistent error messages save more support hours than any dashboard.
Contracts that age well
Treat breaking changes like product incidents: version explicitly, document deprecations with dates, and publish migration notes. Predictable pagination matters too—prefer cursors for large streams; use offset only when datasets are bounded. Always return stable sort keys so clients do not see duplicates when data shifts under them.
- Idempotency keys on writes that create money or inventory side effects
- Machine-readable error codes plus human-readable messages
- Consistent datetime, money, and nullability conventions
- OpenAPI that matches production—not an aspirational wiki page
Operability is part of design
Log correlation IDs end-to-end so when a partner opens a ticket you can trace the request without guessing. Rate limits should be documented and returned in headers. Good API design is equal parts schema taste and support empathy.
