tRPC

tRPC enables end-to-end typesafe APIs for TypeScript without requiring schemas or code generation. Type safety flows automatically from server procedure definitions to React hooks and client calls.

Documentation

• Docs: https://trpc.io/llms.txt

Key Capabilities

tRPC ships with built-in support for patterns that commonly require external libraries:

• Subscriptions: Real-time updates via WebSockets or Server-Sent Events — no separate pub/sub package needed (wsLink, httpSubscriptionLink)
• Request batching: Multiple procedure calls in a single HTTP request via httpBatchLink — the recommended default link used in all official quickstart setups (must be explicitly configured in the client's links option)
• Data transformers: Serialize complex types (Date, BigInt, Map) end-to-end via superjson transformer option — no manual serialization layer
• Server-side caller: Call procedures directly in tests or server code without HTTP overhead using createCallerFactory()
• Middleware chaining: Compose reusable auth, logging, and rate-limiting logic with t.middleware() — result passed through typed ctx augmentation

Best Practices

Always use appRouter type export, never the router value, for client-side type inference. Importing the router value on the client creates a bundle dependency on server code. Export only the type: export type AppRouter = typeof appRouter. Agents often import the full router by mistake, which can bundle server-only code or cause circular imports.

Procedures are not callable unless registered on a router. A procedure built with .query() or .mutation() is a definition, not a live endpoint. It must be added to a router object passed to createHTTPServer or the Next.js adapter. Agents sometimes call createCallerFactory on a bare procedure instead of a router.

Context is created per-request — never mutate shared state inside createContext. Each request receives a fresh context object. Storing request-scoped data (user session, request ID) in a module-level variable instead of returning it from createContext causes data leakage between concurrent requests.

Nest sub-routers under named keys, not flat. Use t.router({ posts: postRouter, users: userRouter }) to create typed namespaces. Use t.mergeRouters(a, b) only when you intentionally want a flat merge with no nesting — otherwise type inference for namespaced routes breaks.

Set abortOnUnmount: true on the tRPC React provider to cancel in-flight requests on component unmount. By default tRPC does not abort queries when a component unmounts, which causes state updates on unmounted components and potential race conditions in fast navigation scenarios.