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Exploring the Difference Between Public and Private Environment Variables in Next.js

Environment variables play a crucial role in modern web development, helping manage sensitive information such as API keys, database credentials, and configuration settings. In Next.js, environment variables are divided into two categories: public and private. Understanding the distinction between these categories is essential for building secure and efficient web applications. This article explores the key differences, use cases, and best practices for handling public and private environment variables in Next.js.

What Are Environment Variables in Next.js?

next js environment variables allow developers to store configuration values outside of their codebase. These variables can adapt an application to different environments, such as development, staging, or production, without requiring code changes. However, because Next.js operates on both the server and the client, managing the visibility of these variables is critical to avoid accidental exposure of sensitive information.

Private Environment Variables

Private environment variables are intended to be used exclusively on the server. They are not included in the client-side JavaScript bundle and cannot be accessed by client-side code. This makes them suitable for storing sensitive information such as:

• Database connection strings.
• Backend API keys.
• Third-party service secrets.

Defining Private Variables

Private variables can be defined in .env files at the root of your Next.js project

Using Private Variables

These variables can be accessed in server-side code, such as in API routes, getServerSideProps, or getStaticProps


Public Environment Variables

Public environment variables are designed to be accessible in both server-side and client-side code. However, they must be explicitly marked as public by prefixing them with NEXT_PUBLIC_. These variables are included in the client-side JavaScript bundle, so they should never contain sensitive information.

Defining Public Variables

To define public variables, use the NEXT_PUBLIC_ prefix:

Using Public Variables

Public variables can be accessed from anywhere in your application

These variables are useful for:

• Frontend configurations.
• Public-facing API endpoints.
• Application metadata.

Key Differences Between Public and Private Variables

Best Practices for Managing Public and Private Variables

1. Never Expose Sensitive Data Publicly
   Only use public variables for non-sensitive information.
2. Use Prefixes Consistently
   Always prefix public variables with NEXT_PUBLIC_ to avoid accidental exposure.
3. Securely Configure Variables for Production
   Use your hosting provider’s secret management features to configure private variables securely.
4. Validate Environment Variables
   Add runtime checks to ensure that required variables are defined to prevent deployment issues.
5. Restart the Development Server
   After modifying .env files, restart the development server to ensure changes are loaded.

Public and private environment variables in Next.js serve distinct purposes, each tailored to specific use cases. By understanding their differences and following best practices, developers can maintain a secure and efficient development process. Properly managing environment variables ensures sensitive information remains protected while enabling flexibility and adaptability across environments. Whether your project is simple or complex, this distinction is vital for building robust, scalable applications in Next.js.