api-and-interface-designlisted

# API and Interface Design ## Overview Design stable, well-documented interfaces that are hard to misuse. Good interfaces make the right thing easy and the wrong thing hard. This applies to REST APIs, GraphQL schemas, module boundaries, component props, and any surface where one piece of code talks to another. ## When to Use - Designing new API endpoints - Defining module boundaries or contracts between teams - Creating component prop interfaces - Establishing database schema that informs API shape - Changing existing public interfaces ## Core Principles ### 1. Contract First Define the interface before implementing it. The contract is the spec — implementation follows. ```typescript // Define the contract first interface TaskAPI { // Creates a task and returns the created task with server-generated fields createTask(input: CreateTaskInput): Promise<Task>; // Returns paginated tasks matching filters listTasks(params: ListTasksParams): Promise<PaginatedResult<Task>>; // Returns a single task or throws NotFoundError getTask(id: string): Promise<Task>; // Partial update — only provided fields change updateTask(id: string, input: UpdateTaskInput): Promise<Task>; // Idempotent delete — succeeds even if already deleted deleteTask(id: string): Promise<void>; } ``` ### 2. Consistent Error Semantics Pick one error strategy and use it everywhere: ```typescript // REST: HTTP status codes + structured error body // Every error response follows the same