Nuxt/docs/2.guide/3.going-further/10.runtime-config.md

title	description
Runtime Config	Nuxt provides a runtime config API to expose configuration and secrets within your application.

Exposing

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.

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.

const runtimeConfig = useRuntimeConfig()

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

::tip Public runtime config is accessible in Vue templates with $config.public. ::

Serialization

Your runtime config will be serialized before being passed to Nitro. This means that anything that cannot be serialized and then deserialized (such as functions, Sets, Maps, and so on), should not be set in your nuxt.config.

Instead of passing non-serializable objects or functions into your application from your nuxt.config, you can place this code in a Nuxt or Nitro plugin or middleware.

Environment Variables

The most common way to provide configuration is by using Environment Variables.

::note Nuxi CLI has built-in support for reading your .env file in development, build and generate. But when you run your built server, your .env file will not be read. :read-more{to="/docs/guide/directory-structure/env"} ::

Runtime config values are automatically replaced by matching environment variables at runtime.

There are two key requirements:

1. Your desired variables must be defined in your nuxt.config. This ensures that arbitrary environment variables are not exposed to your application code.

2. Only a specially-named environment variable can override a runtime config property. That is, an uppercase environment variable starting with NUXT_ which uses _ to separate keys and case changes.

::warning Setting the default of runtimeConfig values to differently named environment variables (for example setting myVar to process.env.OTHER_VARIABLE) will only work during build-time and will break on runtime. It is advised to use environment variables that match the structure of your runtimeConfig object. ::

Example

NUXT_API_SECRET=api_secret_token
NUXT_PUBLIC_API_BASE=https://nuxtjs.org

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
    }
  },
})

Reading

Vue App

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

::important The behavior is different between the client-side and server-side:

• On client-side, only keys in runtimeConfig.public are available, and the object is both writable and reactive.

• On server-side, the entire runtime config is available on the server-side, but it is read-only to avoid context sharing. ::

<script setup lang="ts">
const config = useRuntimeConfig()

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

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

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

Plugins

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

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.

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

::note Giving the event as argument to useRuntimeConfig is optional, but it is recommended to pass it to get the runtime config overwritten by environment variables at runtime for server routes. ::

Typing Runtime Config

Nuxt tries to automatically generate a typescript interface from provided runtime config using unjs/untyped.

But it is also possible to type your runtime config manually:

declare module 'nuxt/schema' {
  interface RuntimeConfig {
    apiSecret: string
  }
  interface PublicRuntimeConfig {
    apiBase: string
  }
}
// It is always important to ensure you import/export something when augmenting a type
export {}

::note nuxt/schema is provided as a convenience for end-users to access the version of the schema used by Nuxt in their project. Module authors should instead augment @nuxt/schema. ::