#Configure Rsbuild

Rsbuild provides a wide range of configuration options with sensible defaults for most use cases. In most scenarios, you can use Rsbuild out of the box without any configuration.

When you need to customize build behavior, use these configuration options.

#Configuration structure

The configuration structure of Rsbuild looks like this:

export default {
  plugins: [
    // configure Rsbuild plugins
  ],
  dev: {
    // options for local development
  },
  html: {
    // options for HTML generation
  },
  tools: {
    // options for the low-level tools
  },
  output: {
    // options for build outputs
  },
  resolve: {
    // options for module resolution
  },
  source: {
    // options for input source code
  },
  server: {
    // options for the Rsbuild server,
    // will take effect during local development and preview
  },
  security: {
    // options for Web security
  },
  performance: {
    // options for build performance and runtime performance
  },
  moduleFederation: {
    // options for module federation
  },
  environments: {
    // define different Rsbuild configurations for each environment
  },
};

You can find detailed descriptions of all configs on the Configure Overview page.

#Configuration file

When you use the CLI of Rsbuild, Rsbuild will automatically read the configuration file in the root directory of the current project and resolve it in the following order:

• rsbuild.config.mjs
• rsbuild.config.ts
• rsbuild.config.js
• rsbuild.config.cjs
• rsbuild.config.mts
• rsbuild.config.cts

We recommend using the .mjs or .ts format for the configuration file and importing the defineConfig utility function from @rsbuild/core. It provides friendly TypeScript type hints and autocompletion, which can help you avoid errors in the configuration.

For example, in rsbuild.config.ts, you can define the Rsbuild resolve.alias configuration:

import { defineConfig } from '@rsbuild/core';

export default defineConfig({
  resolve: {
    alias: {
      '@common': './src/common',
    },
  },
});

If you are developing a non-TypeScript project, you can use the .mjs format for the configuration file:

import { defineConfig } from '@rsbuild/core';

export default defineConfig({
  resolve: {
    alias: (opts) => {
      opts['@common'] = './src/common';
    },
  },
});

#Specify config file

Rsbuild CLI uses the --config option to specify the config file, which can be set to a relative path or an absolute path.

For example, if you need to use the rsbuild.prod.config.mjs file when running build, you can add the following scripts to package.json:

{
  "scripts": {
    "build": "rsbuild build --config rsbuild.prod.config.mjs"
  }
}

You can also abbreviate the --config option to -c:

rsbuild build -c rsbuild.prod.config.mjs

#Specify config loader

Rsbuild provides three ways to load configuration files:

• jiti (Default): When you use a configuration file with the .ts, .mts, and .cts extensions, Rsbuild will use jiti to load configuration files, providing interoperability between ESM and CommonJS. The behavior of module resolution differs slightly from the native behavior of Node.js.

• native: Use Node.js native loader to load the configuration file. This can ensure that the module resolution behavior is consistent with the native behavior of Node.js and has better performance. This requires that your JavaScript runtime already natively supports TypeScript.

  For example, Node.js v22.6.0+ already natively supports TypeScript, you can use the following command to use the Node.js native loader to load the configuration file:

  # Node.js >= v22.18.0
  # No need to set --experimental-strip-types
  npx rsbuild build --config-loader native
  
  # Node.js v22.6.0 - v22.17.1
  # Need to set --experimental-strip-types
  NODE_OPTIONS="--experimental-strip-types" npx rsbuild build --config-loader native

• auto: Use Node.js's native loader to load configuration files first, fallback to using jiti if it fails.

#About Node.js native loader

When using Node.js's native loader, please note the following limitations:

1. When importing JSON files, you need to use import attributes:

   import pkgJson from './package.json' with { type: 'json' }; // ✅ Correct
   import pkgJson from './package.json'; // ❌ Incorrect

2. When importing TypeScript files, you need to include the .ts extension:

   import baseConfig from './rsbuild.base.config.ts'; // ✅ Correct
   import baseConfig from './rsbuild.base.config'; // ❌ Incorrect

See Node.js - Running TypeScript Natively for more details.

#Using environment variables

In the configuration file, you can use Node.js environment variables such as process.env.NODE_ENV to dynamically set different configurations:

import { defineConfig } from '@rsbuild/core';

export default defineConfig({
  resolve: {
    alias: {
      '@request':
        process.env.NODE_ENV === 'development'
          ? './src/request.dev.js'
          : './src/request.prod.js',
    },
  },
});

#Export function

Rsbuild supports the export of a function in the config file, where you can dynamically compute the config and return it to Rsbuild.

import { defineConfig } from '@rsbuild/core';

export default defineConfig(({ env, command, envMode }) => ({
  resolve: {
    alias: {
      '@foo': env === 'development' ? './src/foo.dev.ts' : './src/foo.prod.ts',
    },
  },
}));

The function accepts the following parameters:

#env

• Type: string
• Default: process.env.NODE_ENV

The current running environment.

• When running rsbuild dev, the default value of env is development.
• When running rsbuild build or rsbuild preview, the default value of env is production.

#envMode

• Type: string
• Default: process.env.NODE_ENV

The current value of the CLI parameter --env-mode.

For example, when running rsbuild build --env-mode test, the value of envMode is test.

#command

• Type: string

The current running CLI command, such as dev, build, preview.

#Export async function

Rsbuild also supports the export of an async function in the config file, where you can perform some async operations:

import { defineConfig } from '@rsbuild/core';

export default defineConfig(async ({ env, command }) => {
  const result = await someAsyncFunction();

  return {
    html: {
      title: result,
    },
  };
});

#Merge configurations

You can use the mergeRsbuildConfig function exported by @rsbuild/core to merge multiple configurations.

import { defineConfig, mergeRsbuildConfig } from '@rsbuild/core';

const config1 = defineConfig({
  dev: { port: '3000' },
});
const config2 = defineConfig({
  dev: { port: '3001' },
});

// { dev: { port: '3001' }
export default mergeRsbuildConfig(config1, config2);

#Debug the config

You can enable Rsbuild's debug mode by adding the DEBUG=rsbuild environment variable when executing a build.

DEBUG=rsbuild pnpm dev

In debug mode, Rsbuild will write the Rsbuild config to the dist directory, which is convenient for developers to view and debug.

config inspection completed, open the following files to view the content:

   - Rsbuild config: /Project/demo/dist/.rsbuild/rsbuild.config.mjs
   - Rspack config (web): /Project/demo/dist/.rsbuild/rspack.config.web.mjs

Open the generated /dist/.rsbuild/rsbuild.config.mjs file to see the complete content of the Rsbuild config.

For a complete introduction to debug mode, see the Debug Mode chapter.