Next.js 16 Applications

Build Next.js 16 applications correctly with distinctive design.

Critical Breaking Changes (Next.js 16)

1. params and searchParams are Now Promises

THIS IS THE MOST COMMON MISTAKE.

typescript

// WRONG - Next.js 15 pattern (WILL FAIL)
export default function Page({ params }: { params: { id: string } }) {
  return <div>ID: {params.id}</div>
}

// CORRECT - Next.js 16 pattern
export default async function Page({
  params,
}: {
  params: Promise<{ id: string }>
}) {
  const { id } = await params
  return <div>ID: {id}</div>
}

2. Client Components Need use() Hook

typescript

"use client"
import { use } from "react"

export default function ClientPage({
  params,
}: {
  params: Promise<{ id: string }>
}) {
  const { id } = use(params)
  return <div>ID: {id}</div>
}

3. searchParams Also Async

typescript

export default async function Page({
  searchParams,
}: {
  searchParams: Promise<{ page?: string }>
}) {
  const { page } = await searchParams
  return <div>Page: {page ?? "1"}</div>
}

Core Patterns

Project Setup

bash

npx create-next-app@latest my-app --typescript --tailwind --eslint
cd my-app

# Add shadcn/ui
npx shadcn@latest init
npx shadcn@latest add button form dialog table sidebar

App Router Layout

typescript

// app/layout.tsx
export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body className="min-h-screen">
        {children}
      </body>
    </html>
  )
}

Dynamic Routes

typescript

// app/tasks/[id]/page.tsx
export default async function TaskPage({
  params,
}: {
  params: Promise<{ id: string }>
}) {
  const { id } = await params
  const task = await getTask(id)

  return (
    <main>
      <h1>{task.title}</h1>
    </main>
  )
}

Server Actions

typescript

// app/actions.ts
"use server"

import { revalidatePath } from "next/cache"

export async function createTask(formData: FormData) {
  const title = formData.get("title") as string

  await db.insert(tasks).values({ title })

  revalidatePath("/tasks")
}

// Usage in component
<form action={createTask}>
  <input name="title" />
  <button type="submit">Create</button>
</form>

API Routes

typescript

// app/api/tasks/route.ts
import { NextResponse } from "next/server"

export async function GET() {
  const tasks = await db.select().from(tasksTable)
  return NextResponse.json(tasks)
}

export async function POST(request: Request) {
  const body = await request.json()
  const task = await db.insert(tasksTable).values(body).returning()
  return NextResponse.json(task, { status: 201 })
}

Middleware → proxy.ts

typescript

// proxy.ts (replaces middleware.ts in Next.js 16)
import { NextRequest } from "next/server"

export function proxy(request: NextRequest) {
  // Authentication check
  const token = request.cookies.get("token")
  if (!token && request.nextUrl.pathname.startsWith("/dashboard")) {
    return Response.redirect(new URL("/login", request.url))
  }
}

export const config = {
  matcher: ["/dashboard/:path*"],
}

Data Fetching

Server Component (Default)

typescript

// This runs on the server - can use async/await directly
async function TaskList() {
  const tasks = await fetch("https://api.example.com/tasks", {
    cache: "no-store", // SSR, or
    // next: { revalidate: 60 } // ISR
  }).then(r => r.json())

  return (
    <ul>
      {tasks.map(task => <li key={task.id}>{task.title}</li>)}
    </ul>
  )
}

Client Component

typescript

"use client"

import useSWR from "swr"

const fetcher = (url: string) => fetch(url).then(r => r.json())

export function ClientTaskList() {
  const { data, error, isLoading } = useSWR("/api/tasks", fetcher)

  if (isLoading) return <div>Loading...</div>
  if (error) return <div>Error loading tasks</div>

  return (
    <ul>
      {data.map(task => <li key={task.id}>{task.title}</li>)}
    </ul>
  )
}

Project Structure

app/
├── layout.tsx           # Root layout
├── page.tsx             # Home page
├── globals.css          # Global styles
├── api/                 # API routes
│   └── tasks/route.ts
├── tasks/
│   ├── page.tsx         # /tasks
│   └── [id]/page.tsx    # /tasks/:id
├── actions.ts           # Server actions
└── proxy.ts             # Request proxy (middleware)
components/
├── ui/                  # shadcn/ui components
└── task-list.tsx        # App components
lib/
├── db.ts                # Database connection
└── utils.ts             # Utilities

Next.js DevTools MCP

Use the next-devtools-mcp server for runtime diagnostics and development automation.

Setup

bash

claude mcp add next-devtools npx next-devtools-mcp@latest

Or in settings.json:

json

{
  "mcpServers": {
    "next-devtools": {
      "type": "stdio",
      "command": "npx",
      "args": ["next-devtools-mcp@latest"]
    }
  }
}

Available Tools

Tool	Purpose
`init`	Establish context with available tools and best practices
`nextjs_docs`	Search and fetch official Next.js documentation
`browser_eval`	Automate browser testing with Playwright
`nextjs_index`	Discover running Next.js dev servers
`nextjs_call`	Execute MCP tools on running dev servers
`upgrade_nextjs_16`	Automated upgrade with codemods
`enable_cache_components`	Configure Cache Components for Next.js 16

Key Use Cases

1. Get Real-time Errors

"What build errors are there in my Next.js app?"
"Show me TypeScript errors in the current project"

2. Debug Runtime Issues

"Check the dev server logs for errors"
"What runtime errors are happening on the dashboard page?"

3. Upgrade Assistance

"Upgrade this project to Next.js 16"
"Enable cache components for this app"

4. Documentation Lookup

"How do I use the Image component in Next.js 16?"
"What's the correct way to handle dynamic routes?"

Next.js 16 MCP Endpoint

Next.js 16+ exposes a built-in MCP endpoint at http://localhost:3000/_next/mcp (or your dev server port). The devtools MCP automatically discovers and connects to running servers.

Verification

Run: python3 scripts/verify.py

Expected: ✓ building-nextjs-apps skill ready

If Verification Fails

Check: references/ folder has nextjs-16-patterns.md
Stop and report if still failing

Related Skills

styling-with-shadcn - UI components for Next.js apps
fetching-library-docs - Latest Next.js docs: --library-id /vercel/next.js --topic routing
configuring-better-auth - OAuth/SSO for Next.js apps

References

references/nextjs-16-patterns.md - Complete Next.js 16 patterns
references/frontend-design.md - Aesthetic guidelines for distinctive UI
references/datetime-patterns.md - UTC/timezone handling for datetime-local inputs

Search AI Tools

building-nextjs-apps

Install this agent skill to your Project

SKILL.md

Next.js 16 Applications

Critical Breaking Changes (Next.js 16)

1. params and searchParams are Now Promises

2. Client Components Need use() Hook

3. searchParams Also Async

Core Patterns

Project Setup

App Router Layout

Dynamic Routes

Server Actions

API Routes

Middleware → proxy.ts

Data Fetching

Server Component (Default)

Client Component

Project Structure

Next.js DevTools MCP

Setup

Available Tools

Key Use Cases

Next.js 16 MCP Endpoint

Verification

If Verification Fails

Related Skills

References