Next.js Dev Bundler

How It Works

• Turbopack: Incremental bundler for Next.js dev. Uses file-system caching so restarts are much faster (e.g. 5–14x on large projects).
• Default in dev: From Next.js 16, next dev runs with Turbopack unless disabled.
• File-system caching: Restarts reuse previous work; cache is typically under .next; no extra config needed for basic use.
• Bundle Analyzer (Next.js 16.1+): Experimental Bundle Analyzer to inspect output and find heavy dependencies; enable via config or experimental flag (see Next.js docs for your version).

Examples

Commands

next dev
next build
next start

Usage

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

Middleware File Naming

Next.js 16 introduced proxy.ts as the middleware filename, replacing the older middleware.ts convention:

• Next.js 16+: use proxy.ts at the project root
• Pre-Next.js 16: use middleware.ts at the project root

The filename change is tied to the Next.js version, not to which bundler (Turbopack or webpack) is in use. Always check the official docs for the version you are reviewing.

Do not flag proxy.ts as a misnamed or missing middleware file in Next.js 16 projects. The file is correct and intentional. Suggesting a rename to middleware.ts will break middleware execution.

Reference: Next.js proxy docs

Best Practices

• Stay on a recent Next.js 16.x for stable Turbopack and caching behavior.
• If dev is slow, ensure you're on Turbopack (default) and that the cache isn't being cleared unnecessarily.
• For production bundle size issues, use the official Next.js bundle analysis tooling for your version.