How to Migrate a Next.js Application from Version 14 to Version 15

Introduction

Next.js 15 introduces improvements in performance, caching behavior, routing stability, and TurboPack integration. Applications built with Next.js 14 can usually upgrade smoothly, but the process still requires validating configuration changes and removing deprecated patterns. This guide provides a clear, step‑by‑step workflow to migrate an existing Next.js 14 application to Next.js 15.

Prerequisites

Before starting, ensure you have:

• A running Next.js 14 application
• Node.js 18.18+, 20+, or 22+
• Git for version control
• Familiarity with the App Router and component rendering model

1. Review Release Notes

Before upgrading, consult the official Next.js release notes for the latest changes and guidance: Next.js Release Notes: Next.js Documentation

Before upgrading, review the official Next.js release notes to check:

• Deprecated configuration values
• Updates to routing systems
• Changes to the rendering and caching pipeline

Understanding these changes helps prevent migration‑related issues.

2. Update Core Dependencies

Refer to the official Next.js documentation for updated installation instructions: Next.js Documentation

To upgrade the framework, update Next.js, React, and React DOM: Upgrade Next.js, React, and React DOM:

npm install next@latest react@latest react-dom@latest

npm install next@latest react@latest react-dom@latest

Or with Yarn:

yarn add next@latest react@latest react-dom@latest

yarn add next@latest react@latest react-dom@latest

Run:

npm install

npm install

This ensures all peer dependencies align with the latest version.

3. Update next.config.js

Next.js 15 introduces refined defaults and removes older experimental flags.

A clean configuration looks like:

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  experimental: {
    serverActions: true
  }
};

module.exports = nextConfig;

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  experimental: {
    serverActions: true
  }
};

module.exports = nextConfig;

Remove deprecated options such as legacy TurboPack flags.

4. Validate App Router Structure

For a deeper understanding of the App Router fundamentals used in both Next.js 14 and 15, see our guide: Mastering Next.js App Router

If your application uses the App Router, verify:

• Each segment contains valid page.tsx and layout.tsx files
• Server Components do not import client‑only APIs
• Client Components include a top‑line "use client"

Example:

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

export default function Toggle() {
  const [open, setOpen] = useState(false);
  return <button onClick={() => setOpen(!open)}>Toggle</button>;
}

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

export default function Toggle() {
  const [open, setOpen] = useState(false);
  return <button onClick={() => setOpen(!open)}>Toggle</button>;
}

Next.js 15 enforces component boundaries more strictly.

5. Update the Metadata System

For a full overview of the Metadata API and its capabilities, review the official Next.js Metadata documentation Next.js 15 continues to support the Metadata API. Ensure your application uses: Next.js 15 continues to support the Metadata API. Ensure your application uses:

• The metadata export in layout.tsx
• Dynamic metadata via generateMetadata

Example:

export const metadata = {
  title: "Dashboard",
  description: "User dashboard"
};

export const metadata = {
  title: "Dashboard",
  description: "User dashboard"
};

Remove legacy implementations such as using Head imports.

6. Resolve Build Errors and Warnings

Start the development server:

npm run dev

npm run dev

Common errors include:

• Server Components importing hooks
• Incorrect path imports
• Deprecated metadata usage

Carefully review warnings, as they often indicate required changes.

7. Review Middleware and Route Handlers

Check your middleware.ts file and ensure matchers follow updated conventions:

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

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

Validate Route Handlers using the route.ts pattern.

8. Test API Routes

For more details on Route Handlers and best practices, check the Next.js API routing documentation, Confirm your API routes under app/api/.../route.ts: Confirm your API routes under app/api/.../route.ts:

export async function GET() {
  return Response.json({ status: "ok" });
}

export async function GET() {
  return Response.json({ status: "ok" });
}

Test streaming responses and caching behavior to ensure compatibility.

9. Build and Deploy

Finally, run:

npm run build

npm run build

Resolve any warnings and deploy using your preferred environment.

Conclusion

Migrating from Next.js 14 to 15 is straightforward when following a structured approach. By updating dependencies, reviewing configuration changes, validating App Router conventions, and testing API routes, you ensure your application benefits from improved performance and stability. Regularly upgrading your Next.js version keeps your project secure, maintainable, and ready for future enhancements.