Designing APIs Contract-First

Contract-first design is the cheapest way to unblock a team. When the request/response shapes, status codes, and error schemas are agreed up front, frontend and backend can build against the same source of truth simultaneously.

I document the contract, generate types from it, and let both sides consume those types. Drift becomes a compile error instead of a 2 a.m. incident. Error schemas deserve as much care as the happy path — consistent error shapes make clients dramatically simpler.

The contract is also where you encode rate limits, pagination, and versioning conventions. Decide those once, centrally, and every endpoint inherits good behavior.