env (next.config) & environment variables
Inlines environment variables at build time and exposes public ones.
Syntax
env: { KEY: process.env.KEY } // or NEXT_PUBLIC_* in .envParameters
| Name | Type | Required | Description |
|---|---|---|---|
env | Record<string, string> | No | Build-time variables inlined into the bundle. |
Returns
NextConfig — Inlined env values; merged with .env files.
Examples
# .env.local
DATABASE_URL=postgres://localhost/app
NEXT_PUBLIC_API_URL=https://api.example.com
// Server-only: available in Server Components/actions/handlers
const db = connect(process.env.DATABASE_URL)
// Client-exposed: must be prefixed NEXT_PUBLIC_
export function ApiBadge() {
return <span>{process.env.NEXT_PUBLIC_API_URL}</span>
}
// next.config.js — legacy explicit inlining
const nextConfig = {
env: {
BUILD_ID: process.env.BUILD_ID,
},
}
module.exports = nextConfig
Notes
Variables in `.env*` files are loaded automatically. Only those
prefixed `NEXT_PUBLIC_` are inlined into client bundles; everything
else is server-only — never put secrets in `NEXT_PUBLIC_*`. Values
are inlined at build time, so changing them requires a rebuild. Use
`.env.local` for secrets (gitignored).