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

# tools.swc

- **Type:**

```ts
type ToolsSwc =
  | Rspack.SwcLoaderOptions
  | ((config: Rspack.SwcLoaderOptions) => Rspack.SwcLoaderOptions | undefined);
```

- **Default:**

```js
const defaultOptions = {
  jsc: {
    externalHelpers: true,
    parser: {
      tsx: false,
      syntax: 'typescript',
      decorators: true,
    },
  },
  experimental: {
    cacheRoot: './node_modules/.cache/.swc',
    keepImportAttributes: true,
  },
  isModule: 'unknown',
  env: {
    // Read the browserslist configuration of the project
    targets: browserslist,
  },
  // ...some other conditional options
};
```

You can set the options of [builtin:swc-loader](https://rspack.rs/guide/features/builtin-swc-loader) through `tools.swc`.

> Refer to [Configure SWC](/guide/configuration/swc.md) for more details.

## Object type

`tools.swc` can be configured as an object, this object will be deeply merged with the built-in `builtin:swc-loader` option.

```ts title="rsbuild.config.ts"
export default {
  tools: {
    swc: {
      jsc: {
        externalHelpers: false,
      },
    },
  },
};
```

## Function type

`tools.swc` can also be configured as a function, this function takes one argument, which is the built-in `builtin:swc-loader` option. You can modify this object then return a new config. For example:

```ts title="rsbuild.config.ts"
export default {
  tools: {
    swc: (config) => {
      config.jsc ||= {};
      config.jsc.externalHelpers = false;
      return config;
    },
  },
};
```

:::tip
The object returned by the `tools.swc` function will be used directly as the final `builtin:swc-loader` option, and will not be merged with the built-in `builtin:swc-loader` option anymore.
:::

## Configuration conflicts

In the SWC configuration, `jsc.target` (which specifies the ECMAScript version, such as `es2015`) and `env` cannot coexist.

To avoid conflicts, Rsbuild adopts the following handling strategies:

- If Rsbuild detects that you have manually set `jsc.target` in `tools.swc`, it will automatically remove the built-in `env.targets`.
- If [output.polyfill](/config/output/polyfill.md) is configured, Rsbuild will force set `env.mode`. In this case, you cannot use `jsc.target`.