src/
├── trpc/
│   ├── trpc.ts          # tRPC initialization (t.router, t.procedure)
│   ├── context.ts       # Request context type
│   ├── router.ts        # Root router (merges all sub-routers)
│   ├── users.ts         # User procedures
│   └── posts.ts         # Post procedures
├── lib/
│   └── trpc-client.ts   # React client setup
└── server.ts            # tRPC adapter integration

Server Setup

Initialize tRPC (Once Per App)

// src/trpc/trpc.ts
import { initTRPC, TRPCError } from "@trpc/server"
import type { Context } from "./context"

const t = initTRPC.context<Context>().create()

export const router = t.router
export const procedure = t.procedure
export const publicProcedure = t.procedure

Define Context

// src/trpc/context.ts
export interface Context {
  user?: { id: string; role: "user" | "admin" }
  db: DatabaseClient
}

export function createContext({ req }: { req: Request }): Context {
  const token = req.headers.get("authorization")
  return {
    user: token ? verifyToken(token) : undefined,
    db: getDbClient(),
  }
}

Root Router

// src/trpc/router.ts
import { router } from "./trpc"
import { usersRouter } from "./users"
import { postsRouter } from "./posts"

export const appRouter = router({
  users: usersRouter,
  posts: postsRouter,
})

export type AppRouter = typeof appRouter

Procedures

Query (Read Data)

import { z } from "zod"
import { router, publicProcedure } from "./trpc"

export const usersRouter = router({
  // Simple query
  list: publicProcedure.query(async ({ ctx }) => {
    return ctx.db.users.findMany()
  }),

  // Query with input
  getById: publicProcedure
    .input(z.object({ id: z.string() }))
    .query(async ({ ctx, input }) => {
      const user = await ctx.db.users.findUnique({ where: { id: input.id } })
      if (!user) {
        throw new TRPCError({ code: "NOT_FOUND", message: "User not found" })
      }
      return user
    }),
})

Mutation (Write Data)

export const postsRouter = router({
  create: publicProcedure
    .input(z.object({
      title: z.string().min(1).max(100),
      content: z.string(),
      published: z.boolean().default(false),
    }))
    .mutation(async ({ ctx, input }) => {
      return ctx.db.posts.create({ data: input })
    }),

  update: publicProcedure
    .input(z.object({
      id: z.string(),
      title: z.string().optional(),
      content: z.string().optional(),
    }))
    .mutation(async ({ ctx, input }) => {
      const { id, ...data } = input
      return ctx.db.posts.update({ where: { id }, data })
    }),

  delete: publicProcedure
    .input(z.object({ id: z.string() }))
    .mutation(async ({ ctx, input }) => {
      await ctx.db.posts.delete({ where: { id: input.id } })
      return { success: true }
    }),
})

Subscription (Real-time with SSE)

import { observable } from "@trpc/server/observable"

export const eventsRouter = router({
  onUpdate: publicProcedure
    .input(z.object({ channelId: z.string() }))
    .subscription(({ input }) => {
      return observable<{ message: string }>((emit) => {
        const handler = (data: { message: string }) => {
          emit.next(data)
        }

        eventEmitter.on(input.channelId, handler)

        return () => {
          eventEmitter.off(input.channelId, handler)
        }
      })
    }),
})

Middleware

Base Procedure Pattern (Recommended)

// src/trpc/trpc.ts
import { initTRPC, TRPCError } from "@trpc/server"

const t = initTRPC.context<Context>().create()

// 1. Public procedure with logging
const loggedProcedure = t.procedure.use(async ({ path, type, next }) => {
  const start = Date.now()
  const result = await next()
  console.log(`${type} ${path} - ${Date.now() - start}ms`)
  return result
})

// 2. Authenticated procedure (extends logged)
export const authedProcedure = loggedProcedure.use(async ({ ctx, next }) => {
  if (!ctx.user) {
    throw new TRPCError({ code: "UNAUTHORIZED" })
  }
  return next({
    ctx: { ...ctx, user: ctx.user }, // user is now non-null
  })
})

// 3. Admin procedure (extends authed)
export const adminProcedure = authedProcedure.use(async ({ ctx, next }) => {
  if (ctx.user.role !== "admin") {
    throw new TRPCError({ code: "FORBIDDEN", message: "Admin access required" })
  }
  return next({ ctx })
})

export const router = t.router
export const publicProcedure = loggedProcedure

Using Protected Procedures

import { router, authedProcedure, adminProcedure } from "./trpc"

export const adminRouter = router({
  // Requires authentication
  getProfile: authedProcedure.query(({ ctx }) => {
    return ctx.db.users.findUnique({ where: { id: ctx.user.id } })
  }),

  // Requires admin role
  deleteUser: adminProcedure
    .input(z.object({ userId: z.string() }))
    .mutation(({ ctx, input }) => {
      return ctx.db.users.delete({ where: { id: input.userId } })
    }),
})

Context Extension with Middleware

// Add organization context
const withOrganization = t.middleware(async ({ ctx, input, next }) => {
  const orgId = (input as { organizationId?: string })?.organizationId
  if (!orgId) {
    throw new TRPCError({ code: "BAD_REQUEST", message: "organizationId required" })
  }

  const org = await ctx.db.organizations.findUnique({ where: { id: orgId } })
  if (!org) {
    throw new TRPCError({ code: "NOT_FOUND", message: "Organization not found" })
  }

  return next({
    ctx: { ...ctx, organization: org },
  })
})

export const orgProcedure = authedProcedure.use(withOrganization)

Error Handling

TRPCError Codes

Code	HTTP Status	Use Case
`BAD_REQUEST`	400	Invalid input
`UNAUTHORIZED`	401	Not logged in
`FORBIDDEN`	403	Insufficient permissions
`NOT_FOUND`	404	Resource doesn't exist
`CONFLICT`	409	Resource conflict
`PRECONDITION_FAILED`	412	Condition not met
`TOO_MANY_REQUESTS`	429	Rate limited
`INTERNAL_SERVER_ERROR`	500	Server error

Throwing Errors

import { TRPCError } from "@trpc/server"

// Basic error
throw new TRPCError({
  code: "NOT_FOUND",
  message: "Post not found",
})

// With cause (preserves stack trace)
try {
  await riskyOperation()
} catch (err) {
  throw new TRPCError({
    code: "INTERNAL_SERVER_ERROR",
    message: "Operation failed",
    cause: err,
  })
}

Global Error Handler

// In server setup
const handler = createHTTPHandler({
  router: appRouter,
  createContext,
  onError: ({ error, type, path, input, ctx }) => {
    console.error(`tRPC Error: ${type} ${path}`, {
      code: error.code,
      message: error.message,
      input,
      userId: ctx?.user?.id,
    })

    // Report to error tracking
    if (error.code === "INTERNAL_SERVER_ERROR") {
      reportError(error)
    }
  },
})

React Client Setup

v11 New Pattern (Recommended)

// src/lib/trpc-client.ts
import { createTRPCContext } from "@trpc/tanstack-react-query"
import { httpBatchLink } from "@trpc/client"
import type { AppRouter } from "@/trpc/router"

export const { TRPCProvider, useTRPC, useTRPCClient } = createTRPCContext<AppRouter>()

export function createTRPCClient() {
  return {
    links: [
      httpBatchLink({
        url: "/api/trpc",
        headers: () => ({
          authorization: getAuthToken(),
        }),
      }),
    ],
  }
}

Provider Setup

// src/main.tsx
import { QueryClient, QueryClientProvider } from "@tanstack/react-query"
import { TRPCProvider, createTRPCClient } from "@/lib/trpc-client"

const queryClient = new QueryClient()
const trpcClient = createTRPCClient()

function App() {
  return (
    <TRPCProvider client={trpcClient} queryClient={queryClient}>
      <QueryClientProvider client={queryClient}>
        <Router />
      </QueryClientProvider>
    </TRPCProvider>
  )
}

Classic Pattern (Still Supported)

// src/lib/trpc-client.ts
import { createTRPCReact } from "@trpc/react-query"
import { httpBatchLink } from "@trpc/client"
import type { AppRouter } from "@/trpc/router"

export const trpc = createTRPCReact<AppRouter>()

export function createTRPCClient() {
  return trpc.createClient({
    links: [
      httpBatchLink({
        url: "/api/trpc",
      }),
    ],
  })
}

React Usage

v11 New Pattern

import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query"
import { useTRPC } from "@/lib/trpc-client"

function UserProfile({ userId }: { userId: string }) {
  const trpc = useTRPC()
  const queryClient = useQueryClient()

  // Query
  const { data: user, isLoading } = useQuery(
    trpc.users.getById.queryOptions({ id: userId })
  )

  // Mutation with cache invalidation
  const updateUser = useMutation({
    ...trpc.users.update.mutationOptions(),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: trpc.users.getById.queryKey({ id: userId }) })
    },
  })

  if (isLoading) return <div>Loading...</div>

  return (
    <div>
      <h1>{user?.name}</h1>
      <button onClick={() => updateUser.mutate({ id: userId, name: "New Name" })}>
        Update
      </button>
    </div>
  )
}

Classic Pattern

import { trpc } from "@/lib/trpc-client"

function UserProfile({ userId }: { userId: string }) {
  const utils = trpc.useUtils()

  // Query
  const { data: user, isLoading } = trpc.users.getById.useQuery({ id: userId })

  // Mutation
  const updateUser = trpc.users.update.useMutation({
    onSuccess: () => {
      utils.users.getById.invalidate({ id: userId })
    },
  })

  if (isLoading) return <div>Loading...</div>

  return (
    <div>
      <h1>{user?.name}</h1>
      <button onClick={() => updateUser.mutate({ id: userId, name: "New Name" })}>
        Update
      </button>
    </div>
  )
}

Optimistic Updates

const updatePost = useMutation({
  ...trpc.posts.update.mutationOptions(),
  onMutate: async (newData) => {
    await queryClient.cancelQueries({ queryKey: trpc.posts.getById.queryKey({ id: newData.id }) })

    const previous = queryClient.getQueryData(trpc.posts.getById.queryKey({ id: newData.id }))

    queryClient.setQueryData(
      trpc.posts.getById.queryKey({ id: newData.id }),
      (old) => ({ ...old, ...newData })
    )

    return { previous }
  },
  onError: (err, newData, context) => {
    queryClient.setQueryData(
      trpc.posts.getById.queryKey({ id: newData.id }),
      context?.previous
    )
  },
})

Input Validation with Zod

Common Patterns

import { z } from "zod"

// Pagination
const paginationInput = z.object({
  page: z.number().int().min(1).default(1),
  limit: z.number().int().min(1).max(100).default(20),
})

// Filters
const filterInput = z.object({
  search: z.string().optional(),
  status: z.enum(["active", "inactive", "all"]).default("all"),
  sortBy: z.enum(["createdAt", "name", "updatedAt"]).default("createdAt"),
  sortOrder: z.enum(["asc", "desc"]).default("desc"),
})

// Combined
export const listUsersInput = paginationInput.merge(filterInput)

// Usage
list: publicProcedure
  .input(listUsersInput)
  .query(async ({ ctx, input }) => {
    const { page, limit, search, status, sortBy, sortOrder } = input
    // ...
  }),

Complex Validation

const createUserInput = z.object({
  email: z.string().email(),
  password: z.string().min(8).regex(/[A-Z]/, "Must contain uppercase"),
  profile: z.object({
    name: z.string().min(1).max(100),
    bio: z.string().max(500).optional(),
    avatar: z.string().url().optional(),
  }),
  preferences: z.record(z.string(), z.unknown()).optional(),
})

Advanced Patterns

Batch Requests

// Client automatically batches requests made in same tick
const [users, posts, settings] = await Promise.all([
  trpc.users.list.query(),
  trpc.posts.list.query(),
  trpc.settings.get.query(),
])
// → Single HTTP request with all 3 procedures

File Uploads (v11)

// Server
upload: publicProcedure
  .input(z.object({
    file: z.instanceof(File),
    metadata: z.object({ name: z.string() }),
  }))
  .mutation(async ({ input }) => {
    const buffer = await input.file.arrayBuffer()
    // Process file...
  }),

// Client - use FormData link
import { unstable_formDataLink } from "@trpc/client"

Type Inference

import type { inferRouterInputs, inferRouterOutputs } from "@trpc/server"
import type { AppRouter } from "@/trpc/router"

type RouterInputs = inferRouterInputs<AppRouter>
type RouterOutputs = inferRouterOutputs<AppRouter>

// Usage
type CreateUserInput = RouterInputs["users"]["create"]
type User = RouterOutputs["users"]["getById"]

Gotchas and Tips

Export type only: Use export type { AppRouter } to prevent server code in client bundles
Initialize once: Call initTRPC once per app, not per router file
Base procedures: Create 2-3 reusable base procedures (public, authed, admin)
Context flows through: Middleware can narrow context types for downstream procedures
Zod schemas: Define input schemas at the top of files for reusability
Error codes matter: Use appropriate codes for proper HTTP status mapping
Batch by default: httpBatchLink batches requests automatically
TypeScript 5.7+: Required for v11, enable strict mode

Migration from v10 to v11

v10	v11
`trpc.users.getById.useQuery()`	`useQuery(trpc.users.getById.queryOptions())`
`trpc.users.create.useMutation()`	`useMutation(trpc.users.create.mutationOptions())`
`utils.users.invalidate()`	`queryClient.invalidateQueries({ queryKey: trpc.users.queryKey() })`
WebSocket subscriptions	SSE subscriptions (recommended)

trpc

tRPC Skill

Quick Reference

Project Structure