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# server.tsconfigPath

- **Type:** `string`
- **Default:** `<appDirectory>/tsconfig.json`

Specifies the tsconfig file used by server-side TypeScript processes.

This option affects:

- BFF / API compilation (`@modern-js/plugin-bff`)
- Custom server compilation (`*.ts` files under `server/`)
- Runtime Node-native TypeScript registration, such as SSR, `modern.config.ts`, and `.ts` files under `config/`

When this option is not set, `<appDirectory>/tsconfig.json` is used by default.

## When to use

Use this option when frontend and server-side code need different TypeScript configurations.

For example, the frontend can use `moduleResolution: "Bundler"`, while the server side uses `moduleResolution: "NodeNext"` for type resolution of conditional exports or subpath exports.

## Example

The example below uses `tsconfig.server.json` as the file name. You can use another name in your project.

Add `<appDirectory>/tsconfig.server.json`:

```jsonc title="tsconfig.server.json"
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "target": "ES2022",
    "lib": ["ESNext"],
    "types": ["node"],
    "esModuleInterop": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  },
  "include": ["api", "shared", "server", "config", "modern.config.ts"]
}
```

Specify this file in `modern.config.ts`:

```ts title="modern.config.ts"
export default defineConfig({
  server: {
    tsconfigPath: './tsconfig.server.json',
  },
});
```

## Notes

- `tsconfigPath` is resolved relative to `appDirectory`. Absolute paths are also supported.
- It is recommended to inherit shared options such as `paths` from the root tsconfig through `extends`, instead of maintaining them in multiple files.
- If the configured file does not exist, the runtime TypeScript setup will throw an error at startup.