Install

# NPM
npm install --save-dev webpack-bundle-analyzer
# Yarn
yarn add -D webpack-bundle-analyzer

Usage (as a plugin)

const { BundleAnalyzerPlugin } = require("webpack-bundle-analyzer");

module.exports = {
  plugins: [new BundleAnalyzerPlugin()],
};

It will create an interactive treemap visualization of the contents of all your bundles.

This module will help you:

1. Realize what's really inside your bundle
2. Find out what modules make up the most of its size
3. Find modules that got there by mistake
4. Optimize it!

And the best thing is it supports minified bundles! It parses them to get real size of bundled modules. And it also shows their gzipped, Brotli, or Zstandard sizes!

Options (for plugin)

new BundleAnalyzerPlugin(options?: object)

Name	Type	Description
analyzerMode	One of: server, static, json, disabled	Default: server. In server mode analyzer will start HTTP server to show bundle report. In static mode single HTML file with bundle report will be generated. In json mode single JSON file with bundle report will be generated. In disabled mode you can use this plugin to just generate Webpack Stats JSON file by setting generateStatsFile to true.
analyzerHost	{String}	Default: 127.0.0.1. Host that will be used in server mode to start HTTP server.
analyzerPort	{Number} or auto	Default: 8888. Port that will be used in server mode to start HTTP server. If analyzerPort is auto, the operating system will assign an arbitrary unused port
analyzerUrl	{Function} called with { listenHost: string, listenHost: string, boundAddress: server.address}. server.address comes from Node.js	Default: http://${listenHost}:${boundAddress.port}. The URL printed to console with server mode.
reportFilename	{String}	Default: report.html. Path to bundle report file that will be generated in static mode. It can be either an absolute path or a path relative to a bundle output directory (which is output.path in webpack config).
reportTitle	{String|function}	Default: function that returns pretty printed current date and time. Content of the HTML title element; or a function of the form () => string that provides the content.
defaultSizes	One of: stat, parsed, gzip, brotli	Default: parsed. Module sizes to show in report by default. Size definitions section describes what these values mean.
compressionAlgorithm	One of: gzip, brotli, zstd	Default: gzip. Compression type used to calculate the compressed module sizes.
openAnalyzer	{Boolean}	Default: true. Automatically open report in default browser.
generateStatsFile	{Boolean}	Default: false. If true, webpack stats JSON file will be generated in bundle output directory
statsFilename	{String}	Default: stats.json. Name of webpack stats JSON file that will be generated if generateStatsFile is true. It can be either an absolute path or a path relative to a bundle output directory (which is output.path in webpack config).
statsOptions	null or {Object}	Default: null. Options for stats.toJson() method. For example you can exclude sources of your modules from stats file with source: false option. See more options here.
excludeAssets	{null|pattern|pattern[]} where pattern equals to {String|RegExp|function}	Default: null. Patterns that will be used to match against asset names to exclude them from the report. If pattern is a string it will be converted to RegExp via new RegExp(str). If pattern is a function it should have the following signature (assetName: string) => boolean and should return true to exclude matching asset. If multiple patterns are provided asset should match at least one of them to be excluded.
logLevel	One of: info, warn, error, silent	Default: info. Used to control how much details the plugin outputs.

Absolute output paths

reportFilename and statsFilename can be absolute paths. Use absolute paths when you want the generated report or stats file to be written outside webpack's output.path. Relative paths are resolved against the bundle output directory.

const path = require("node:path");
const { BundleAnalyzerPlugin } = require("webpack-bundle-analyzer");

module.exports = {
  plugins: [
    new BundleAnalyzerPlugin({
      analyzerMode: "static",
      reportFilename: path.resolve(__dirname, "reports/report.html"),
      generateStatsFile: true,
      statsFilename: path.resolve(__dirname, "reports/stats.json"),
    }),
  ],
};

Usage (as a CLI utility)

You can analyze an existing bundle if you have a webpack stats JSON file.

You can generate it using BundleAnalyzerPlugin with generateStatsFile option set to true or with this simple command:

webpack --profile --json > stats.json

If you're on Windows and using PowerShell, you can generate the stats file with this command to avoid BOM issues:

webpack --profile --json | Out-file 'stats.json' -Encoding OEM

Then you can run the CLI tool.

webpack-bundle-analyzer bundle/output/path/stats.json

Options (for CLI)

webpack-bundle-analyzer <bundleStatsFile> [bundleDir] [options]

Arguments are documented below:

bundleStatsFile

Path to webpack stats JSON file

bundleDir

Directory containing all generated bundles.

options

  -V, --version                   output the version number
  -m, --mode <mode>               Analyzer mode. Should be `server`, `static` or `json`.
                                  In `server` mode analyzer will start HTTP server to show bundle report.
                                  In `static` mode single HTML file with bundle report will be generated.
                                  In `json` mode single JSON file with bundle report will be generated. (default: server)
  -h, --host <host>               Host that will be used in `server` mode to start HTTP server. (default: 127.0.0.1)
  -p, --port <n>                  Port that will be used in `server` mode to start HTTP server. Should be a number or `auto` (default: 8888)
  -r, --report <file>             Path to bundle report file that will be generated in `static` mode. (default: report.html)
  -t, --title <title>             String to use in title element of html report. (default: pretty printed current date)
  -s, --default-sizes <type>      Module sizes to show in treemap by default.
                                  Possible values: stat, parsed, gzip, brotli, zstd (default: parsed)
  --compression-algorithm <type>  Compression algorithm that will be used to calculate the compressed module sizes.
                                  Possible values: gzip, brotli, zstd (default: gzip)
  -O, --no-open                   Don't open report in default browser automatically.
  -e, --exclude <regexp>          Assets that should be excluded from the report.
                                  Can be specified multiple times.
  -l, --log-level <level>         Log level.
                                  Possible values: debug, info, warn, error, silent (default: info)
  -h, --help                      output usage information

Size definitions

webpack-bundle-analyzer reports three values for sizes. defaultSizes can be used to control which of these is shown by default. The different reported sizes are:

stat

This is the "input" size of your files, before any transformations like minification.

It is called "stat size" because it's obtained from Webpack's stats object.

parsed

This is the "output" size of your files. If you're using a Webpack plugin such as Uglify, then this value will reflect the minified size of your code.

gzip

This is the size of running the parsed bundles/modules through gzip compression.

brotli

This is the size of running the parsed bundles/modules through Brotli compression.

zstd

This is the size of running the parsed bundles/modules through Zstandard compression. (Node.js 22.15.0+ is required for this feature)

Selecting Which Chunks to Display

When opened, the report displays all of the Webpack chunks for your project. It's possible to filter to a more specific list of chunks by using the sidebar or the chunk context menu.

Sidebar

The Sidebar Menu can be opened by clicking the > button at the top left of the report. You can select or deselect chunks to display under the "Show chunks" heading there.

Chunk Context Menu

The Chunk Context Menu can be opened by right-clicking or Ctrl-clicking on a specific chunk in the report. It provides the following options:

• Hide chunk: Hides the selected chunk
• Hide all other chunks: Hides all chunks besides the selected one
• Show all chunks: Un-hides any hidden chunks, returning the report to its initial, unfiltered view

Troubleshooting

I don't see gzip or parsed sizes, it only shows stat size

It happens when webpack-bundle-analyzer analyzes files that don't actually exist in your file system, for example when you work with webpack-dev-server that keeps all the files in RAM. If you use webpack-bundle-analyzer as a plugin you won't get any errors, however if you run it via CLI you get the error message in terminal:

Error parsing bundle asset "your_bundle_name.bundle.js": no such file
No bundles were parsed. Analyzer will show only original module sizes from stats file.

To get more information about it you can read issue #147.

Other tools

• Statoscope - Webpack bundle analyzing tool to find out why a certain module was bundled (and more features, including interactive treemap)

Maintainers

Yuriy Grunin

Vesa Laakso

Contributing

Check out CONTRIBUTING.md for instructions on contributing :tada: