tRPC With Next.js 14: End-to-End Type Safety Without REST or GraphQL

tRPC eliminates the API layer. Your frontend calls server functions directly with full TypeScript types across the boundary. No schema generation, no code gen, no OpenAPI spec.

Here's how to set it up with Next.js 14 App Router.

Why tRPC

Traditional REST:

// Server defines route
// Client fetches with fetch()
// Types manually kept in sync (or schema gen)
// Runtime errors when they drift

tRPC:

// Define procedure on server
// Call it on client like a function
// Types flow automatically
// TypeScript catches mismatches at compile time

Installation

npm install @trpc/server @trpc/client @trpc/react-query @tanstack/react-query zod

Server Setup

// server/trpc.ts
import { initTRPC, TRPCError } from '@trpc/server'
import { auth } from '@/lib/auth'
import { ZodError } from 'zod'

const t = initTRPC.context<{ userId: string | null }>().create({
  errorFormatter({ shape, error }) {
    return {
      ...shape,
      data: {
        ...shape.data,
        zodError: error.cause instanceof ZodError ? error.cause.flatten() : null
      }
    }
  }
})

export const router = t.router
export const publicProcedure = t.procedure
export const protectedProcedure = t.procedure.use(async ({ ctx, next }) => {
  if (!ctx.userId) throw new TRPCError({ code: 'UNAUTHORIZED' })
  return next({ ctx: { userId: ctx.userId } })
})

// server/context.ts
import { auth } from '@/lib/auth'

export async function createContext() {
  const session = await auth()
  return { userId: session?.user?.id ?? null }
}

export type Context = Awaited<ReturnType<typeof createContext>>

Defining Routers

// server/routers/post.ts
import { z } from 'zod'
import { router, publicProcedure, protectedProcedure } from '../trpc'
import { db } from '@/lib/db'

export const postRouter = router({
  list: publicProcedure
    .input(z.object({ limit: z.number().min(1).max(100).default(10) }))
    .query(async ({ input }) => {
      return db.post.findMany({ take: input.limit, orderBy: { createdAt: 'desc' } })
    }),

  byId: publicProcedure
    .input(z.object({ id: z.string() }))
    .query(async ({ input }) => {
      const post = await db.post.findUnique({ where: { id: input.id } })
      if (!post) throw new TRPCError({ code: 'NOT_FOUND' })
      return post
    }),

  create: protectedProcedure
    .input(z.object({
      title: z.string().min(1).max(100),
      content: z.string().min(1).max(10000)
    }))
    .mutation(async ({ input, ctx }) => {
      return db.post.create({
        data: { ...input, authorId: ctx.userId }
      })
    }),

  delete: protectedProcedure
    .input(z.object({ id: z.string() }))
    .mutation(async ({ input, ctx }) => {
      const post = await db.post.findFirst({ where: { id: input.id, authorId: ctx.userId } })
      if (!post) throw new TRPCError({ code: 'FORBIDDEN' })
      return db.post.delete({ where: { id: input.id } })
    })
})

// server/root.ts
import { router } from './trpc'
import { postRouter } from './routers/post'
import { userRouter } from './routers/user'

export const appRouter = router({
  post: postRouter,
  user: userRouter
})

export type AppRouter = typeof appRouter

Next.js Route Handler

// app/api/trpc/[trpc]/route.ts
import { fetchRequestHandler } from '@trpc/server/adapters/fetch'
import { appRouter } from '@/server/root'
import { createContext } from '@/server/context'

const handler = (request: Request) =>
  fetchRequestHandler({
    endpoint: '/api/trpc',
    req: request,
    router: appRouter,
    createContext
  })

export { handler as GET, handler as POST }

Client Setup

// lib/trpc.ts
import { createTRPCReact } from '@trpc/react-query'
import type { AppRouter } from '@/server/root'

export const trpc = createTRPCReact<AppRouter>()

// app/providers.tsx
'use client'
import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
import { httpBatchLink } from '@trpc/client'
import { trpc } from '@/lib/trpc'
import { useState } from 'react'

export function Providers({ children }: { children: React.ReactNode }) {
  const [queryClient] = useState(() => new QueryClient())
  const [trpcClient] = useState(() => trpc.createClient({
    links: [httpBatchLink({ url: '/api/trpc' })]
  }))

  return (
    <trpc.Provider client={trpcClient} queryClient={queryClient}>
      <QueryClientProvider client={queryClient}>
        {children}
      </QueryClientProvider>
    </trpc.Provider>
  )
}

Using in Client Components

'use client'
import { trpc } from '@/lib/trpc'

export function PostList() {
  const { data, isLoading } = trpc.post.list.useQuery({ limit: 20 })
  const createPost = trpc.post.create.useMutation({
    onSuccess: () => utils.post.list.invalidate()
  })
  const utils = trpc.useUtils()

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

  return (
    <div>
      {data?.map(post => <div key={post.id}>{post.title}</div>)}
      <button onClick={() => createPost.mutate({ title: 'New Post', content: '...' })}>
        Create Post
      </button>
    </div>
  )
}
// TypeScript knows: data is Post[] | undefined
// createPost.mutate() input is fully typed
// Errors are typed TRPCClientError

When to Use tRPC vs Server Actions

Scenario	Choice
Form submissions	Server Actions
Data fetching in client components	tRPC
Mobile app backend	tRPC
Real-time subscriptions	tRPC (with subscriptions)
Simple CRUD in Server Components	Prisma directly

Starter Kit With tRPC

The Ship Fast Skill Pack includes a /trpc skill that scaffolds the full tRPC setup for your project -- routers, context, client, and providers.

Ship Fast Skill Pack -- $49 one-time -- 10 Claude Code skills including full tRPC scaffolding.

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