tRPC Router Generator

tRPC is a TypeScript library that lets you build fully type-safe APIs without a schema or code generation step. You define your server procedures in TypeScript, and your client gets automatic type inference — including input validation, return types, and error types — all end-to-end.

A router is a collection of procedures (think: API endpoints) grouped together. You compose routers hierarchically: an appRouter might include a userRouter, postRouter, and authRouter. Each sub-router is created with router() and combined at the top level.

Queries are for reading data — they use GET semantics, support caching, and can be called with useQuery() on the client. Mutations are for writes and side effects — they're called imperatively with useMutation().mutate() and are never cached. Use query for fetching, mutation for creating/updating/deleting.

Zod is a TypeScript-first schema validation library. tRPC uses Zod schemas for .input() and .output() validation — input schemas automatically validate incoming data (throwing a TRPCError on invalid input), and output schemas validate return types. The schemas also drive full TypeScript inference on both server and client.

Create a protected procedure by wrapping the base procedure with middleware that checks auth context. In the generated code, use protectedProcedure instead of publicProcedure. Your middleware should throw a TRPCError({ code: 'UNAUTHORIZED' }) if the session is missing.

A caller lets you call tRPC procedures directly on the server — useful in getServerSideProps, API routes, or server components. Create one with createCallerFactory(appRouter)(ctx) and call procedures like regular async functions without HTTP overhead.