Next.js and Turbopack

Next.js 16+ uses Turbopack by default for local development: an incremental bundler written in Rust that significantly speeds up dev startup and hot updates.

When to use

• Turbopack (default dev): Use for day-to-day development. Faster cold starts and HMR, especially in large applications.
• Webpack (legacy dev): Use only if you hit a Turbopack bug or rely on a webpack-specific plugin in dev. Disable it with

--webpack (or --no-turbopack depending on your Next.js version; check the docs for your version).

• Production: Production build behavior (next build) may use Turbopack or webpack depending on the Next.js version;

check the official Next.js documentation for your version.

Use this when developing or debugging Next.js 16+ applications, diagnosing slow dev startup or HMR, or optimizing production bundles.

How it works

• Turbopack: The incremental bundler for Next.js dev. It uses a file system cache, so restarts are much faster (for

example, 5-14x in large projects).

• Default in dev: From Next.js 16 onward, next dev runs with Turbopack unless it is disabled.
• File system cache: Restarts reuse previous work; the cache is usually under .next, and no extra configuration is

needed for basic use.

• Bundle Analyzer (Next.js 16.1+): An experimental Bundle Analyzer for inspecting the output and finding heavy

dependencies; enable it via config or an experimental flag (see the Next.js documentation for your version).

Examples

#### Commands

To run local development with Turbopack:

next dev

To create a production build:

next build

To start the production server after building:

next start

#### Usage

Run next dev for local development with Turbopack. Use the Bundle Analyzer to optimize code-splitting and trim large dependencies (see the Next.js documentation). Prefer the App Router and server components where possible.

Best practices

• Stay on a current Next.js 16.x version for stable Turbopack and caching behavior.
• If dev is slow, make sure you are on Turbopack (the default) and that the cache is not being cleared unnecessarily.
• For production bundle size issues, use the official Next.js bundle analysis tools for your version.