Backend tRPC

Design and implement end-to-end type-safe APIs using tRPC with proper router organization, procedure definitions, input validation with Zod schemas, context management, and middleware. Use this skill when creating or modifying tRPC router files like server/routers/*.ts, src/server/api/routers/*.ts, *.router.ts, or any files containing tRPC procedure definitions, queries, and mutations. Use this when defining tRPC routers with .query() for read operations and .mutation() for write operations, implementing input validation using Zod schemas with .input(z.object({...})) for type-safe runtime validation of all procedure parameters, creating and organizing reusable sub-routers by feature or domain (user router, post router, comment router) and composing them into a main app router using mergeRouters or router nesting, setting up tRPC context in createContext functions to provide request-scoped data like user sessions, database connections, or authentication state to all procedures, implementing tRPC middleware with .use() for cross-cutting concerns like authentication, authorization, logging, rate limiting, or error handling, defining procedure-level permissions and access control logic to protect sensitive operations, handling errors by throwing TRPCError instances with specific error codes like BAD_REQUEST, UNAUTHORIZED, FORBIDDEN, NOT_FOUND, or INTERNAL_SERVER_ERROR, leveraging TypeScript's automatic type inference for end-to-end type safety that flows from server procedures to client-side hooks, configuring tRPC server adapters for Next.js API routes, Express servers, or standalone HTTP servers, integrating tRPC with React Query or TanStack Query on the frontend for data fetching and mutations, implementing batch operations to combine multiple tRPC calls and reduce network overhead, organizing router files by feature domain for maintainability and scalability, exporting the AppRouter type for client-side type safety, creating reusable procedure builders for common patterns like protected procedures or admin-only procedures, and ensuring all tRPC procedures follow consistent patterns for error handling and validation.