Migrate React + Vite to Next.js 16

Overview

This skill helps AI agents:

• Audit existing React+Vite projects (routing, state management, data fetching, dependencies)
• Bootstrap a parallel Next.js 16 App Router project with Tailwind, shadcn/ui, and modern tooling
• Translate routes, layouts, components, and data-fetching patterns into idiomatic Server/Client Components
• Migrate environment variables, static assets, and API routes to Next.js 16 conventions (including proxy.ts)
• Optimize & deploy using React Compiler, Turbopack, and platform-specific deployment guidance

This migration preserves UI components while transforming the underlying architecture to leverage SSR, streaming, and Server Actions.

FIRST: Verify React Project Structure

Confirm the project is a React application by checking:

1. react and react-dom in package.json dependencies
2. Presence of vite.config.ts/js, craco.config.js, or webpack.config.js
3. Either src/ directory with components or root-level component files

If none found, STOP — this skill does not apply.

Detect the package manager from the lockfile:

Detect routing system:

• React Router — Check for react-router-dom in dependencies
• TanStack Router — Check for @tanstack/react-router
• Wouter — Check for wouter
• No router — Single-page app with manual navigation

Migration Strategy Overview

Phase 1: Compatibility Audit

1a. Check Critical Dependencies

Generally Compatible: Material-UI, Ant Design, Chakra UI, Radix UI, Headless UI, Zustand, Jotai, Valtio, React Hook Form, Formik, Framer Motion, date-fns, lodash, clsx

Requires Refactoring: Redux/Redux Toolkit (wrap in useRef provider), React Query/TanStack Query (configure for SSR), Apollo Client (SSR setup), SWR (configure for SSR)

Incompatible / Not Needed: react-router-dom, Vite plugins, react-helmet, dotenv

See references/compatibility.md for the full library compatibility matrix.

1b. Analyze Application Architecture

Categorize components by type:

1. Page Components — Top-level routes (Home, About, Dashboard)
2. Layout Components — Shared structure (Header, Sidebar, Footer)
3. UI Components — Reusable elements (Button, Card, Modal)
4. Data Components — Components with API calls/side effects
5. Context Providers — Global state (Theme, Auth, etc.)

Phase 2: Project Initialization

2a. Create Next.js Project Alongside

CRITICAL: Do not delete or modify the existing React project yet. Create Next.js in a parallel directory for gradual migration and easy rollback.

npx create-next-app@latest [project-name]-nextjs --typescript --tailwind --app --src-dir --import-alias "@/*"

Node.js 20.9.0 or later is required for Next.js 16.

2b. Install Core Dependencies

[package-manager] add @radix-ui/react-slot class-variance-authority clsx tailwind-merge
[package-manager-exec] shadcn@latest init
[package-manager] add lucide-react zod react-hook-form @hookform/resolvers

2c. Copy Tailwind Configuration

See references/tailwind-migration.md for detailed examples.

Phase 3: Core File Structure Migration

3a. Convert Routing Structure

Next.js 16: params and searchParams are async Promises — always await them.

// app/blog/[slug]/page.tsx
export default async function BlogPost({
  params,
}: {
  params: Promise<{ slug: string }>;
}) {
  const { slug } = await params;
  return <h1>{slug}</h1>;
}

See references/routing-patterns.md for complex routing scenarios.

3b. Convert Root Layout

Before (React):

// src/App.tsx
function App() {
  return (
    <ThemeProvider>
      <BrowserRouter>
        <Header />
        <Routes>{/* routes */}</Routes>
        <Footer />
      </BrowserRouter>
    </ThemeProvider>
  );
}

After (Next.js 16):

// src/app/layout.tsx
import type { Metadata } from "next";
import { Inter } from "next/font/google";
import "./globals.css";
import { ThemeProvider } from "@/components/providers/theme-provider";

const inter = Inter({ subsets: ["latin"] });

export const metadata: Metadata = {
  title: "My App",
  description: "App description",
};

export default function RootLayout({
  children,
}: {
  children: React.ReactNode;
}) {
  return (
    <html lang="en" suppressHydrationWarning>
      <body className={inter.className}>
        <ThemeProvider>{children}</ThemeProvider>
      </body>
    </html>
  );
}

3c. Migrate Components

Conversion rules:

• No hooks, no events, no browser APIs → Server Component (no directive needed)
• Has useState / useEffect / event handlers → Add 'use client'
• Uses React Context → Wrap in a 'use client' Provider
• Uses React.lazy → Replace with next/dynamic
• Uses <a> for internal links → Replace with next/link
• Uses useNavigate → Replace with useRouter from next/navigation

See references/component-patterns.md for detailed examples.

Phase 4: Data Fetching Transformation

4a. Replace useEffect with Server Components

Before (React):

function UserProfile({ userId }: { userId: string }) {
  const [user, setUser] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch(`/api/users/${userId}`)
      .then((res) => res.json())
      .then((data) => {
        setUser(data);
        setLoading(false);
      });
  }, [userId]);

  if (loading) return <div>Loading...</div>;
  return <div>{user.name}</div>;
}

After (Next.js 16 — Server Component):

async function UserProfile({ userId }: { userId: string }) {
  const user = await fetch(`https://api.example.com/users/${userId}`).then(
    (res) => res.json(),
  );
  return <div>{user.name}</div>;
}

4b. Caching in Next.js 16

Everything is dynamic by default. To opt into caching, use the "use cache" directive:

"use cache";
export default async function ProductsPage() {
  const products = await fetch("https://api.example.com/products").then((r) =>
    r.json(),
  );
  return <ProductList products={products} />;
}

The old fetch(url, { next: { revalidate: 60 } }) and cache: 'force-cache' patterns are deprecated in Next.js 16. Use "use cache" instead.

4c. Server Actions for Mutations

// app/posts/create/actions.ts
"use server";

import { revalidatePath } from "next/cache";
import { redirect } from "next/navigation";

export async function createPost(formData: FormData) {
  const title = formData.get("title") as string;
  await fetch("https://api.example.com/posts", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ title }),
  });
  revalidatePath("/posts");
  redirect("/posts");
}

// app/posts/create/page.tsx
import { createPost } from "./actions";

export default function CreatePostPage() {
  return (
    <form action={createPost}>
      <input name="title" required />
      <button type="submit">Submit</button>
    </form>
  );
}

See references/data-fetching.md for comprehensive patterns.

Phase 5: Environment Variables

See references/environment.md for detailed configuration.

Phase 6: Static Assets

Move src/assets/ → public/. See references/assets.md for optimization.

Phase 7: State Management

Context providers must be 'use client'. All global stores (Zustand, Redux, Jotai) must use a useRef-based provider — never module-level singletons — to prevent state leaking between server requests.

See references/state-management.md for detailed patterns.

Phase 8: API Routes and Proxy

Route Handlers

// app/api/posts/route.ts
import { NextRequest, NextResponse } from "next/server";

export async function GET() {
  const posts = await db.posts.findMany();
  return NextResponse.json(posts);
}

export async function POST(request: NextRequest) {
  const body = await request.json();
  const post = await db.posts.create({ data: body });
  return NextResponse.json(post, { status: 201 });
}

Dynamic route params are async in Next.js 16: { params }: { params: Promise<{ id: string }> } — always await params.

proxy.ts (replaces middleware.ts)

// proxy.ts  ← was middleware.ts in Next.js 13–15
import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";

export function proxy(request: NextRequest) {
  return NextResponse.next();
}

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

See references/api-routes.md for comprehensive examples.

Phase 9: Build Configuration

next.config.ts

import type { NextConfig } from "next";

const config: NextConfig = {
  // React Compiler — stable in Next.js 16
  reactCompiler: true,

  experimental: {
    // Turbopack persistent FS cache — faster cold starts
    turbopackFileSystemCacheForDev: true,
  },

  images: {
    remotePatterns: [{ protocol: "https", hostname: "**.example.com" }],
  },

  async redirects() {
    return [{ source: "/old-path", destination: "/new-path", permanent: true }];
  },
};

export default config;

Turbopack is the default bundler in Next.js 16. Custom webpack configs will not work — rewrite for Turbopack or next.config.ts.

See references/config-options.md for all available options.

Phase 10: Testing and Validation

Feature Parity Checklist

• All routes render correctly
• Navigation between pages works
• Forms submit and handle validation
• Data fetching displays correct content
• Authentication flow works
• Protected routes redirect properly
• Search, filtering, and sorting work
• Dark mode / theme switching works
• Responsive design intact
• Third-party scripts load

Common Migration Issues

See references/troubleshooting.md for solutions.

Phase 11: Deployment

Vercel (Recommended):

npm install -g vercel && vercel login && vercel

Alternatives: Netlify, Cloudflare Pages (@cloudflare/next-on-pages), AWS Amplify, Docker, Node.js server.

See references/deployment.md for platform-specific guides.

Phase 12: Post-Migration Optimization

Convert Client Components to Server Components where possible. Use loading.tsx and <Suspense> for streaming. Add generateMetadata for SEO. Use parallel Promise.all() fetching.

See references/optimization.md for advanced techniques.

Anti-Patterns and Common Mistakes

Do NOT:

• Use useEffect for data fetching in Server Components
• Add 'use client' to every file by default
• Import Server Components into Client Components
• Use window, localStorage, document in Server Components
• Use next: { revalidate } or cache: 'force-cache' — use "use cache" directive instead
• Call cookies() or headers() synchronously — they are async in Next.js 16
• Use a file named middleware.ts — it is now proxy.ts in Next.js 16
• Use module-level store singletons — always wrap in useRef-based providers

DO:

• Default to Server Components
• Add 'use client' only when needed
• Use Server Actions for mutations
• Leverage next/image, next/font, next/script
• Always await params, await cookies(), await headers()
• Follow App Router conventions: layout, loading, error, not-found

Success Criteria

• All pages accessible via Next.js routes
• Build completes without errors
• Lighthouse scores improved (FCP, LCP, TTFB)
• No console errors
• Production deployment successful

Complexity estimate:

• Simple — <10 routes, basic data fetching (2–4 hours)
• Moderate — Multiple routes, React Query/SWR, some global state (1–2 days)
• Complex — 20+ routes, Redux, complex auth, many integrations (3–7 days)