tsconfig

• Type: true | string
• Optional: Yes ✅
• Default: undefined (no tsconfig resolution)

Configures TypeScript configuration file resolution and usage.

Options

Auto-discovery mode (true)

When set to true, Rolldown enables auto-discovery mode (similar to Vite). For each module, both the resolver and transformer will find the nearest tsconfig.json.

If the tsconfig has references and certain conditions are met (the file extension is allowed and the tsconfig's include/exclude patterns don't match the file), then the referenced tsconfigs will be searched for a match. If no match is found, it falls back to the original tsconfig.

export default {
  tsconfig: true,
};

Explicit path (string)

Specifies the path to a specific TypeScript configuration file. You may provide a relative path (resolved relative to cwd) or an absolute path.

export default {
  tsconfig: './tsconfig.json',
};

export default {
  tsconfig: './tsconfig.build.json',
};

export default {
  tsconfig: '/absolute/path/to/tsconfig.json',
};

What's used from tsconfig

When a tsconfig is resolved, Rolldown uses different parts for different purposes:

Resolver

Uses the following for module path mapping:

• compilerOptions.paths: Path mapping for module resolution
• compilerOptions.baseUrl: Base directory for path resolution

Transformer

Uses select compiler options including:

• jsx: JSX transformation mode
• experimentalDecorators: Enable decorator support
• emitDecoratorMetadata: Emit decorator metadata
• verbatimModuleSyntax: Module syntax preservation
• useDefineForClassFields: Class field semantics
• And other TypeScript-specific options

Example

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ESNext",
    "jsx": "react-jsx",
    "baseUrl": ".",
    "paths": {
      "@/*": ["src/*"],
      "@components/*": ["src/components/*"]
    }
  }
}

With this configuration:

• JSX will use React's automatic runtime
• Path aliases like @/utils will resolve to src/utils

Priority

Top-level transform options always take precedence over tsconfig settings:

export default {
  tsconfig: './tsconfig.json', // Has jsx: 'react-jsx'
  transform: {
    jsx: {
      mode: 'classic', // This takes precedence
    },
  },
};

TIP

For TypeScript projects, it's recommended to use tsconfig: true for auto-discovery or specify an explicit path to ensure consistent compilation behavior and enable path mapping.