nextjs-env-variables

Next.js environment variables prefixed with NEXT_PUBLIC_ are exposed to the client-side browser, while unprefixed variables remain securely server-side only. This distinction ensures sensitive keys like STRIPE_SECRET_KEY stay protected during rendering and deployment.

Next.js loads .env files in a specific precedence order, allowing higher-priority files to override lower ones. This mechanism ensures correct configuration loading across development, production, and deployment environments, preventing accidental overrides of critical settings.

Deploying a Next.js app to Vercel requires configuring environment variables directly in the Vercel project settings. You must securely add server-side variables like DATABASE_URL and client-side variables like NEXT_PUBLIC_API_URL to ensure proper application functionality.

Next.js environment variable configuration varies by platform. While local .env files manage development settings, deploying to Vercel, Railway, or Heroku requires inputting variables into each platform's specific dashboard or CLI to ensure correct runtime loading and security.

Next.js environment variables return undefined on the client if they lack the NEXT_PUBLIC_ prefix. Only variables explicitly prefixed with NEXT_PUBLIC_ are statically inlined and exposed to the browser during the build process.

Validating Next.js environment variables involves checking required keys during the build or runtime to prevent missing configuration issues. This validation workflow ensures that critical variables like DATABASE_URL are present and correctly formatted before deployment.