Api And Interface Design

This covers the fundamentals of designing interfaces that won't haunt you later. It's built around Hyrum's Law, the idea that users will depend on every observable behavior whether you document it or not, so you need to be intentional about what you expose. The guidance is practical: validate at boundaries, extend rather than modify, use discriminated unions for variants, and keep error handling consistent across your entire API surface. It works for REST endpoints, GraphQL schemas, module boundaries, or React component props. The examples are TypeScript heavy but the principles apply anywhere code talks to code. Worth using when you're drawing lines between systems or teams.