# Runtime Config

Nuxt provides a runtime config API to expose configuration within your application and server routes, with the ability to update it at runtime by setting environment variables.

## Exposing Runtime Config

To expose config and environment variables to the rest of your app, you will need to define runtime configuration in your `nuxt.config` file, using the [`runtimeConfig` option](/guide/directory-structure/nuxt.config#runtimeconfig).

**Example:**

```ts [nuxt.config.ts]
export default defineNuxtConfig({
  runtimeConfig: {
    // The private keys which are only available within server-side
    apiSecret: '123',
    // Keys within public, will be also exposed to the client-side
    public: {
      apiBase: '/api'
    }
  }
})
```

When adding `apiBase` to the `runtimeConfig.public`, Nuxt adds it to each page payload. We can universally access `apiBase` in both server and browser.

```js
const runtimeConfig = useRuntimeConfig()

console.log(runtimeConfig.apiSecret)
console.log(runtimeConfig.public.apiBase)
```

### Environment Variables

The most common way to provide configuration is by using [Environment Variables](https://medium.com/chingu/an-introduction-to-environment-variables-and-how-to-use-them-f602f66d15fa).

::alert{type=info}
Nuxt CLI has built-in [dotenv](https://github.com/motdotla/dotenv) support in development mode and when running `nuxi build` and `nuxi generate`.

In addition to any process environment variables, if you have a `.env` file in your project root directory, it will be automatically loaded **at build, dev, and generate time**, and any environment variables set there will be accessible within your `nuxt.config` file and modules.

When updating `.env` in development mode, the Nuxt instance is automatically restarted to apply new values to the `process.env`.

However, **after your server is built**, you are responsible for setting environment variables when you run the server. Your `.env` file will not be read at this point. How you do this is different for every environment. On a Linux server, you could pass the environment variables as arguments using the terminal `DATABASE_HOST=mydatabaseconnectionstring node .output/server/index.mjs`. Or you could source your env file using `source .env && node .output/server/index.mjs`.

Note that for a purely static site, it is not possible to set runtime configuration config after your project is prerendered.
::

Runtime config values are automatically replaced by matching environment variables at runtime. For this to work, you _must_ have a fallback value (which can just be an empty string) defined in your `nuxt.config`.

**Example:**

```sh [.env]
NUXT_API_SECRET=api_secret_token
NUXT_PUBLIC_API_BASE=https://nuxtjs.org
```

```ts [nuxt.config.ts]
export default defineNuxtConfig({
  runtimeConfig: {
    apiSecret: '', // can be overridden by NUXT_API_SECRET environment variable
    public: {
      apiBase: '', // can be overridden by NUXT_PUBLIC_API_BASE environment variable
    }
  },
})
```

## Accessing Runtime Config

### Vue App

Within the Vue part of your Nuxt app, you will need to call `useRuntimeConfig()` to access the runtime config.

**Note:** Behavior is different between the client-side and server-side:

- On the client-side, only keys in `public` are available, and the object is both writable and reactive.
The entire runtime config is available on the server-side, but it is read-only to avoid context sharing.

```vue
<template>
  <div>
    <div>Check developer console!</div>
  </div>
</template>

<script setup>
const config = useRuntimeConfig()
console.log('Runtime config:', config)
if (process.server) {
  console.log('API secret:', config.apiSecret)
}
</script>
```

**🛑 Security note:** Be careful not to expose runtime config keys to the client-side by either rendering them or passing them to `useState`.

::alert{icon=👉}
**`useRuntimeConfig` only works during `setup` or `Lifecycle Hooks`**.
::

### Plugins

If you want to use the runtime config within any (custom) plugin, you can use `useRuntimeConfig()` inside of your `defineNuxtPlugin` function.

For Example:

```ts
export default defineNuxtPlugin((nuxtApp) => {
  const config = useRuntimeConfig()
  console.log('API base URL:', config.public.apiBase)
});
```

### Server Routes

You can access runtime config within the server routes as well using `useRuntimeConfig`.

```ts
export default async () => {
  const result = await $fetch('https://my.api.com/test', {
    headers: {
      Authorization: `Bearer ${useRuntimeConfig().apiSecret}`
    }
  })
  return result
}
```

### Manually Typing Runtime Config

Nuxt tries to automatically generate a typescript interface from provided runtime config using [unjs/untyped](https://github.com/unjs/untyped).

It is also possible to type your runtime config manually:

```ts [index.d.ts]
declare module '@nuxt/schema' {
  interface RuntimeConfig {
    apiSecret: string
    public: {
      apiBase: string
    }
  }
}
// It is always important to ensure you import/export something when augmenting a type
export {}
```