package-bundling.mdx

The React Framework

package-bundling.mdx

title: Optimizing package bundling nav_title: Package Bundling description: Learn how to analyze and optimize your application's server and client bundles with the Next.js Bundle Analyzer for Turbopack, and the `@next/bundle-analyzer` plugin for Webpack. related: description: Learn more about optimizing your application for production. links: - app/guides/production-checklist

Bundling is the process of combining your application code and its dependencies into optimized output files for the client and server. Smaller bundles load faster, reduce JavaScript execution time, improve Core Web Vitals, and lower server cold start times.

Next.js automatically optimizes bundles by code splitting, tree-shaking, and other techniques. However, there are some cases where you may need to optimize your bundles manually.

There are two tools for analyzing your application's bundles:

Next.js Bundle Analyzer for Turbopack
@next/bundle-analyzer plugin for Webpack

This guide will walk you through how to use each tool and how to optimize large bundles.

Next.js Bundle Analyzer

Available in v16.1 and later. You can share feedback in the dedicated GitHub discussion and view the demo at turbopack-bundle-analyzer-demo.vercel.sh.

The Next.js Bundle Analyzer is integrated with Turbopack's module graph. You can inspect server and client modules with precise import tracing, making it easier to find large dependencies. Open the interactive Bundle Analyzer demo to explore the module graph.

Step 1: Run the Turbopack Bundle Analyzer

To get started, run the following command and open up the interactive view in your browser.

npx next analyze

yarn next analyze

pnpm next analyze

bunx next analyze

Step 2: Filter and inspect modules

Within the UI, you can filter by route, environment (client or server), and type (JavaScript, CSS, JSON), or search by file:

Step 3: Trace modules with import chains

The treemap shows each module as a rectangle. Where the size of the module is represented by the area of the rectangle.

Click a module to see its size, inspect its full import chain and see exactly where it’s used in your application:

If you want to share the analysis with teammates or compare bundle sizes before/after optimizations, you can skip the interactive view and save the analysis as a static file with the --output flag:

npx next analyze --output

yarn next analyze --output

pnpm next analyze --output

bunx next analyze --output

This command writes the output to .next/diagnostics/analyze. You can copy this directory elsewhere to compare results:

cp -r .next/diagnostics/analyze ./analyze-before-refactor

Export analysis data

Available in v16.4 and later. You can share feedback in the dedicated GitHub discussion and view the demo at turbopack-bundle-analyzer-demo.vercel.sh.

Use next analyze export to stream a saved snapshot as JSON Lines for scripts or AI tools, without rebuilding or starting a server:

npx next analyze --output --snapshot before
npx next analyze export --snapshot before > bundle-graph.jsonl

yarn next analyze --output --snapshot before
yarn next analyze export --snapshot before > bundle-graph.jsonl

pnpm next analyze --output --snapshot before
pnpm next analyze export --snapshot before > bundle-graph.jsonl

bunx next analyze --output --snapshot before
bunx next analyze export --snapshot before > bundle-graph.jsonl

See the CLI reference for export options.

More options are available for the Bundle Analyzer, see Next.js CLI reference docs for the full list.

Give your AI agent access to the bundle analyzer

The next-bundle-optimizer skill gives your AI agent access to the data powering Turbopack's bundle analyzer to automatically identify sources of large client-side bundles that impact your site's initial load performance.

First, install the skill:

npx skills add vercel/next.js --skill next-bundle-optimizer

Then prompt your agent. In audit-only mode, it produces a report without making any changes:

Use the next-bundle-optimizer skill to produce a report of the initial load performance of this site.

You can also tell your agent to fix any issues, and it will optimize your site based on its findings. Or have it focus on a specific route by providing the route in the prompt.

`@next/bundle-analyzer` for Webpack

The @next/bundle-analyzer is a plugin that helps you manage the size of your application bundles. It generates a visual report of the size of each package and their dependencies. You can use the information to remove large dependencies, split, or lazy-load your code.

Step 1: Installation

Install the plugin by running the following command:

pnpm add @next/bundle-analyzer

npm install @next/bundle-analyzer

yarn add @next/bundle-analyzer

bun add @next/bundle-analyzer

Then, add the bundle analyzer's settings to your next.config.js.

/** @type {import('next').NextConfig} */
const nextConfig = {}

const withBundleAnalyzer = require('@next/bundle-analyzer')({
  enabled: process.env.ANALYZE === 'true',
})

module.exports = withBundleAnalyzer(nextConfig)

Step 2: Generating a report

Run the following command to analyze your bundles:

ANALYZE=true npm run build
# or
ANALYZE=true yarn build
# or
ANALYZE=true pnpm build

The report will open three new tabs in your browser, which you can inspect.

Optimizing large bundles

Once you've identified a large module, the solution will depend on your use case. Below are common causes and how to fix them:

Packages with many exports

If you're using a package that exports hundreds of modules (such as icon and utility libraries), you can optimize how those imports are resolved using the optimizePackageImports option in your next.config.js file. This option will only load the modules you actually use, while still giving you the convenience of writing import statements with many named exports.

/** @type {import('next').NextConfig} */
const nextConfig = {
  experimental: {
    optimizePackageImports: ['icon-library'],
  },
}

module.exports = nextConfig

Good to know: Next.js also optimizes some libraries automatically, thus they do not need to be included in the optimizePackageImports list. See the full list of supported packages.

Heavy client workloads

A common cause of large client bundles is doing expensive rendering work in Client Components. This often happens with libraries that exist only to transform data into UI, such as syntax highlighting, chart rendering, or markdown parsing.

If that work does not require browser APIs or user interaction, it can be run in a Server Component.

In this example, a prism based highlighter runs in a Client Component. Even though the final output is just a <code> block, the entire highlighting library is bundled into the client JavaScript bundle:

'use client'

import Highlight from 'prism-react-renderer'
import theme from 'prism-react-renderer/themes/github'

export default function Page() {
  const code = `export function hello() {
    console.log("hi")
  }`

  return (
    <article>
      <h1>Blog Post Title</h1>

      {/* The prism package and its tokenization logic are shipped to the client */}
      <Highlight code={code} language="tsx" theme={theme}>
        {({ className, style, tokens, getLineProps, getTokenProps }) => (
          <pre className={className} style={style}>
            <code>
              {tokens.map((line, i) => (
                <div key={i} {...getLineProps({ line })}>
                  {line.map((token, key) => (
                    <span key={key} {...getTokenProps({ token })} />
                  ))}
                </div>
              ))}
            </code>
          </pre>
        )}
      </Highlight>
    </article>
  )
}

This increases bundle size because the client must download and execute the highlighting library, even though the result is static HTML.

Instead, move the highlighting logic to a Server Component and render the final HTML on the server. The client will only receive the rendered markup.

import { codeToHtml } from 'shiki'

export default async function Page() {
  const code = `export function hello() {
    console.log("hi")
  }`

  // The Shiki package runs on the server and is never bundled for the client.
  const highlightedHtml = await codeToHtml(code, {
    lang: 'tsx',
    theme: 'github-dark',
  })

  return (
    <article>
      <h1>Blog Post Title</h1>

      {/* Client receives plain markup */}
      <pre>
        <code dangerouslySetInnerHTML={{ __html: highlightedHtml }} />
      </pre>
    </article>
  )
}

Opting specific packages out of bundling

Packages imported inside Server Components and Route Handlers are automatically bundled by Next.js.

You can opt specific packages out of bundling using the serverExternalPackages option in your next.config.js.

/** @type {import('next').NextConfig} */
const nextConfig = {
  serverExternalPackages: ['package-name'],
}

module.exports = nextConfig

</AppOnly> <PagesOnly>

External packages that aren't pre-bundled

By default, packages imported into your application are not bundled. This can impact performance if external packages are not pre-bundled, for example, if imported from a monorepo or node_modules.

To bundle specific packages, you can use the transpilePackages option in your next.config.js.

/** @type {import('next').NextConfig} */
const nextConfig = {
  transpilePackages: ['package-name'],
}

module.exports = nextConfig

To automatically bundle all packages, you can use the bundlePagesRouterDependencies option in your next.config.js. This option defaults to false.

/** @type {import('next').NextConfig} */
const nextConfig = {
  bundlePagesRouterDependencies: true,
}

module.exports = nextConfig

Opting specific packages out of bundling

If you identify packages that shouldn't be in the bundle, you can opt specific packages out of automatic bundling using the serverExternalPackages option in your next.config.js:

/** @type {import('next').NextConfig} */
const nextConfig = {
  // Automatically bundle external packages:
  bundlePagesRouterDependencies: true,
  // Opt specific packages out of bundling:
  serverExternalPackages: ['package-name'],
}

module.exports = nextConfig

</PagesOnly>

Version History

Version	Changes
`v16.4.0`	Add `next analyze export` and the `next-bundle-optimizer` skill.

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vercel/next.js / docs / 01-app / 02-guides / package-bundling.mdx

Next.js Bundle Analyzer

Step 1: Run the Turbopack Bundle Analyzer

Step 2: Filter and inspect modules

Step 3: Trace modules with import chains

Step 4: Write output to disk for sharing or diffing

Export analysis data

Give your AI agent access to the bundle analyzer

@next/bundle-analyzer for Webpack

Step 1: Installation

Step 2: Generating a report

Optimizing large bundles

Packages with many exports

Heavy client workloads

Opting specific packages out of bundling

External packages that aren't pre-bundled

Opting specific packages out of bundling

Version History

`@next/bundle-analyzer` for Webpack