Designing Type-Safe APIs with TypeScript

Type safety becomes most valuable at service boundaries. A good API defines clear input, output, and error shapes so clients know what to expect and servers can evolve safely.

TypeScript helps model these contracts, but runtime validation is still required for untrusted input. Validation belongs at the edge of the system: request bodies, webhooks, queues, and third-party responses.

Keep shared types small. Avoid leaking database models directly into public APIs. Stable contracts make refactors cheaper and integration bugs easier to catch.