stack/packages/mosaic/framework/skills/tsdown/references/advanced-rolldown-options.md

Customizing Rolldown Options

Pass options directly to the underlying Rolldown bundler.

Overview

tsdown uses Rolldown as its core bundling engine. You can override Rolldown's input and output options directly for fine-grained control.

Warning: You should be familiar with Rolldown's behavior before overriding options. Refer to the Rolldown Config Options documentation.

Input Options

Using an Object

export default defineConfig({
  inputOptions: {
    cwd: './custom-directory',
  },
});

Using a Function

Dynamically modify options based on the output format:

export default defineConfig({
  inputOptions(inputOptions, format) {
    inputOptions.cwd = './custom-directory';
    return inputOptions;
  },
});

Output Options

Using an Object

export default defineConfig({
  outputOptions: {
    legalComments: 'inline',
  },
});

Using a Function

export default defineConfig({
  outputOptions(outputOptions, format) {
    if (format === 'esm') {
      outputOptions.legalComments = 'inline';
    }
    return outputOptions;
  },
});

Common Use Cases

Preserve Legal Comments

export default defineConfig({
  entry: ['src/index.ts'],
  outputOptions: {
    legalComments: 'inline',
  },
});

Custom Working Directory

export default defineConfig({
  entry: ['src/index.ts'],
  inputOptions: {
    cwd: './packages/my-lib',
  },
});

Format-Specific Options

export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  outputOptions(outputOptions, format) {
    if (format === 'esm') {
      outputOptions.legalComments = 'inline';
    }
    return outputOptions;
  },
});

When to Use

• When tsdown doesn't expose a specific Rolldown option
• For format-specific Rolldown customizations
• For advanced bundling scenarios

Tips

1. Read Rolldown docs before overriding options
2. Use functions for format-specific customization
3. Test thoroughly when overriding defaults
4. Prefer tsdown options when available (e.g., use minify instead of setting it via outputOptions)

Related

• Plugins - Plugin system
• Hooks - Lifecycle hooks
• Config File - Configuration options