Environment Variables

This document is for Next.js versions 9.4 and up. If you’re using an older version of Next.js, upgrade or refer to Environment Variables in next.config.js.

Examples

• Environment Variables

Next.js comes with built-in support for environment variables, which allows you to do the following:

• Use .env.local to load environment variables
• Expose environment variables to the browser

Loading Environment Variables

Next.js has built-in support for loading environment variables from .env.local into process.env.

An example .env.local:

DB_HOST=localhost
DB_USER=myuser
DB_PASS=mypassword

This loads process.env.DB_HOST, process.env.DB_USER, and process.env.DB_PASS into the Node.js environment automatically allowing you to use them in Next.js data fetching methods and API routes.

For example, using getStaticProps:

// pages/index.js
export async function getStaticProps() {
  const db = await myDB.connect({
    host: process.env.DB_HOST,
    username: process.env.DB_USER,
    password: process.env.DB_PASS,
  })
  // ...
}

Note: In order to keep server-only secrets safe, Next.js replaces process.env.* with the correct values at build time. This means that process.env is not a standard JavaScript object, so you’re not able to use object destructuring. Environment variables must be referenced as e.g. process.env.NEXT_PUBLIC_PUBLISHABLE_KEY, not const { NEXT_PUBLIC_PUBLISHABLE_KEY } = process.env.

Note: Next.js will automatically expand variables ($VAR) inside of your .env* files. This allows you to reference other secrets, like so:

# .env
HOSTNAME=localhost
PORT=8080
HOST=http://$HOSTNAME:$PORT

If you are trying to use a variable with a $ in the actual value, it needs to be escaped like so: \$.

For example:

# .env
A=abc

# becomes "preabc"
WRONG=pre$A

# becomes "pre$A"
CORRECT=pre\$A

Exposing Environment Variables to the Browser

By default all environment variables loaded through .env.local are only available in the Node.js environment, meaning they won't be exposed to the browser.

In order to expose a variable to the browser you have to prefix the variable with NEXT_PUBLIC_. For example:

NEXT_PUBLIC_ANALYTICS_ID=abcdefghijk

This loads process.env.NEXT_PUBLIC_ANALYTICS_ID into the Node.js environment automatically, allowing you to use it anywhere in your code. The value will be inlined into JavaScript sent to the browser because of the NEXT_PUBLIC_ prefix. This inlining occurs at build time, so your various NEXT_PUBLIC_ envs need to be set when the project is built.

// pages/index.js
import setupAnalyticsService from '../lib/my-analytics-service'

// NEXT_PUBLIC_ANALYTICS_ID can be used here as it's prefixed by NEXT_PUBLIC_
setupAnalyticsService(process.env.NEXT_PUBLIC_ANALYTICS_ID)

function HomePage() {
  return <h1>Hello World</h1>
}

export default HomePage

Default Environment Variables

In general only one .env.local file is needed. However, sometimes you might want to add some defaults for the development (next dev) or production (next start) environment.

Next.js allows you to set defaults in .env (all environments), .env.development (development environment), and .env.production (production environment).

.env.local always overrides the defaults set.

Note: .env, .env.development, and .env.production files should be included in your repository as they define defaults. .env*.local should be added to .gitignore, as those files are intended to be ignored. .env.local is where secrets can be stored.

Environment Variables on Vercel

When deploying your Next.js application to Vercel, Environment Variables can be configured in the Project Settings.

All types of Environment Variables should be configured there. Even Environment Variables used in Development – which can be downloaded onto your local device afterwards.

If you've configured Development Environment Variables you can pull them into a .env.local for usage on your local machine using the following command:

vercel env pull .env.local

When using the Vercel CLI to deploy make sure you add a .vercelignore that includes files that should not be uploaded, generally these are the same files included in .gitignore.

Test Environment Variables

Apart from development and production environments, there is a 3rd option available: test. In the same way you can set defaults for development or production environments, you can do the same with .env.test file for testing environment (though this one is not so common as the previous two).

This one is useful when running tests with tools like jest or cypress where you need to set specific environment vars only for testing purposes. Test default values will be loaded if NODE_ENV is set to test, though you usually don't need to do this manually as testing tools will address it for you.

There is a small difference between test environment, and both development and production that you need to bear in mind: .env.local won't be loaded, as you expect tests to produce the same results for everyone. This way every test execution will use same env defaults across different executions by ignoring your .env.local (which is intended to override the default set).

Note: similar to Default Environment Variables, .env.test file should be included in your repository, but .env.test.local shouldn't, as .env*.local are intended to be ignored through .gitignore.

While running unit tests you can make sure to load your environment variables the same way Next.js does by leveraging the loadEnvConfig function from the @next/env package.

// The below can be used in a Jest global setup file or similar for your testing set-up
import { loadEnvConfig } from '@next/env'

export default async () => {
  const projectDir = process.cwd()
  loadEnvConfig(projectDir)
}