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Environmental Variables

Overview

Environment variables can be API keys, URLs, database credentials―anything you need to configure a specific environment really. Some are sensitive so they should never be shared as-is in your code or in public, but others are simply useful constants to have around that you only want to define once

Environment Variable Types in Next.js​

Next.js distinguishes between two types of environment variables based on who can access them:

  • Server (backend)

  • Client (browser)

1. 🔒 Server-Only Variables​

These variables are accessible only in server-side code, such as:

  • API routes (/pages/api/*)

  • getServerSideProps

  • Custom server logic

  • Any code that runs on the server

Warning

  • Do not prefix or start Server-Only Variables with NEXT_PUBLIC_.

  • Never expose secrets (API keys, DB credentials) to the client.

  • Available via process.env.[key] only in server-side code.

2. 🌍 Public Variables (Client + Server)​

These variables are available both on the client and the server.

They are typically used for:

  • Public API endpoints

  • Project IDs

  • Analytics keys

  • Any non-sensitive config used in the browser

Warning

If you are working inside Next.js framework then you should have to prefix Public Variables with NEXT_PUBLIC_