Nuxt 3 provides an `app.config` config file to expose reactive configuration within your application with the ability to update it at runtime within lifecycle or using a nuxt plugin and editing it with HMR (hot-module-replacement).
::alert{type=warning}
Do not put any secret values inside `app.config` file. It is exposed to the user client bundle.
::
## Defining App Config
To expose config and environment variables to the rest of your app, you will need to define configuration in `app.config` file.
**Example:**
```ts [app.config.ts]
export default defineAppConfig({
theme: {
primaryColor: '#ababab'
}
})
```
When adding `theme` to the `app.config`, Nuxt uses Vite or Webpack to bundle the code. We can universally access `theme` in both server and browser using [useAppConfig](/api/composables/use-app-config) composable.
```js
const appConfig = useAppConfig()
console.log(appConfig.theme)
```
<!-- TODO: Document module author for extension -->
### Manually Typing App Config
Nuxt tries to automatically generate a typescript interface from provided app config.
