> For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt.

# Build Engine

Modern.js internally encapsulates [Rsbuild](https://v2.rsbuild.rs/), using Rspack as the bundler.

::: tip What is Rsbuild?
Rsbuild is a build tool based on Rspack. It is an enhanced Rspack CLI, easy-to-use, and ready-to-use out of the box.
:::

## Build Architecture

From the building perspective, Modern.js can be divided into three-layers, from top to bottom:

- Upper-level framework: Modern.js.
- Build tool: Rsbuild.
- Bundler: Rspack.


## Build Documentation

The documentation address of Rsbuild is: [https://v2.rsbuild.rs/](https://v2.rsbuild.rs/)

In this documentation, you can learn about the detailed introduction of Rsbuild, and you can also find complete usage guides for various building capabilities.

If you want to understand the use of build configurations, it is recommended that you read the Modern.js documentation first, because the build configurations and defaults in Modern.js are not exactly the same as Rsbuild.

## Build Plugins

In Modern.js, you can register Rspack plugins or Rsbuild plugins:

- Rspack plugins: Configured through [tools.bundlerChain](/configure/app/tools/bundler-chain.md).
- Rsbuild plugins: Configured through [builderPlugins](/configure/app/builder-plugins.md).

## Build Capabilities

Rsbuild provides rich build capabilities, including JavaScript compilation, CSS compilation, static assets processing, code hot update, code compression, TS type checking, and dozens of other capabilities.

We recommend that you read [「Rsbuild - All Features」](https://v2.rsbuild.rs/guide/start/features) to learn about all the features provided by Rsbuild.