What problem does it solve? Public interfaces become permanent promises the moment a consumer depends on them, yet teams routinely leak implementation details, expose unstable types, and ship breaking changes without warning. This Skill enforces contract-first design so every public API — package exports, HTTP/REST, RPC/tRPC, SDKs, module boundaries — is minimal, hard to misuse, and versioned before implementation begins. ## Core Features & Use Cases - Contract-First Design: Write signatures, input/output types, error sets, and invariants before any implementation, making the contract reviewable on its own. - Misuse-Resistant Surfaces: Replace positional booleans and bare primitives with named options objects, branded types, and discriminated unions so invalid calls fail at compile time. - Versioning & Deprecation Discipline: Apply SemVer rules with an additive-first policy and a deprecate-coexist-remove cycle for breaking changes. - Use Case: When designing a new REST endpoint or tRPC router, use this Skill to define the OpenAPI contract, a closed typed error set with stable codes, idempotency keys for mutations, and cursor pagination before writing any handler logic. ## Quick Start Ask the agent to design the public contract for a new user-creation endpoint, including input validation, typed errors, and pagination, before writing the implementation.
