nextjs_warnings.md

Next.js warnings

dotenv-diff includes Next.js-specific rules to catch unsafe or invalid environment variable usage.

This page reflects the currently implemented rule behavior.

1 Client code must use NEXT_PUBLIC_ variables only

When a file is treated as client code ("use client" or Pages Router client files), non-NEXT_PUBLIC_ variables trigger a warning.

"use client";
console.log(process.env.SECRET_TOKEN);

Warning:

Server-only variable accessed from client code

2 import.meta.env is not supported in Next.js

console.log(import.meta.env.PRIVATE_KEY);

Warning:

Next.js uses process.env, not import.meta.env (Vite syntax)

3 Sensitive-looking NEXT_PUBLIC_ names trigger exposure warnings

If a NEXT_PUBLIC_ variable contains SECRET, PRIVATE, or PASSWORD, a warning is produced.

console.log(process.env.NEXT_PUBLIC_SECRET_PASSWORD);

Warning:

Potential sensitive environment variable exposed to the browser

What is allowed

Server files (for example API routes and other server-only code) can use private environment variables without framework warnings.

Summary of rules

• Client code → only NEXT_PUBLIC_*
• import.meta.env → not valid in Next.js
• Sensitive names in NEXT_PUBLIC_* → warning

Best practices

• Use NEXT_PUBLIC_* only for browser-safe values
• Keep secrets in server-only code paths
• Do not use import.meta.env in Next.js projects