makeEnvPublic()

Copy unprefixed variables such as API_URL to NEXT_PUBLIC_API_URL in process.env, so PublicEnvScript and env() can serve them to the browser without renaming anything in your deployment config.

Import

import { makeEnvPublic } from 'next-dynenv'

Signature

function makeEnvPublic(key: string | string[], options?: { logLevel?: 'silent' | 'error' | 'warn' | 'info' }): void

Parameters

Parameter	Type	Description
key	string | string[]	One variable name or a list of names
options.logLevel	'silent' | 'error' | 'warn' | 'info'	Optional. Hides log lines below this level. Unset logs everything.

Behavior

For each key:

process.env[key]	Key	Result	Log
undefined	Any	Skipped	Warning
Set	Starts with NEXT_PUBLIC_	Skipped	Warning
Set	Anything else	process.env.NEXT_PUBLIC_<key> gets the same value, replacing any existing one	Success

The original variable stays in place. An empty string counts as set and gets copied. makeEnvPublic() never throws.

Where to call it

Call it from register() in instrumentation.ts (or src/instrumentation.ts when your app uses a src directory). Next.js runs register() once when each server instance starts, before it handles requests, in every output mode, including output: 'standalone'.

// instrumentation.ts
import { makeEnvPublic } from 'next-dynenv'

export function register() {
    makeEnvPublic(['API_URL', 'APP_NAME'])
}

PublicEnvScript then includes NEXT_PUBLIC_API_URL and NEXT_PUBLIC_APP_NAME, and client components read them with env('NEXT_PUBLIC_API_URL').

next.config is not a substitute

A call at the top of next.config.ts works with next start, which evaluates the config when the server boots. It does nothing at runtime with output: 'standalone': the generated server.js embeds the serialized config and never runs next.config.ts again. Keep the call in instrumentation.ts.

Read the copies through env(), not process.env.NEXT_PUBLIC_API_URL in client code. Next.js inlines literal process.env.NEXT_PUBLIC_* references into client bundles at build time, long before register() runs.

Logging

Success lines go to console.log and warnings to console.warn, each tagged (next-dynenv):

 ✓ Prefixed environment variable 'API_URL' (next-dynenv)
 ⚠ Skipped prefixing environment variable 'REGION'. Variable not in process.env (next-dynenv)
 ⚠ Environment variable 'NEXT_PUBLIC_APP_NAME' is already public (next-dynenv)

logLevel	Success lines	Warnings
Unset	Shown	Shown
'info'	Hidden	Shown
'warn'	Hidden	Shown
'error'	Hidden	Hidden
'silent'	Hidden	Hidden

'info' already hides the success lines, which log one level below it. Leave logLevel unset to see them:

// instrumentation.ts
import { makeEnvPublic } from 'next-dynenv'

export function register() {
    makeEnvPublic(['API_URL', 'APP_NAME'], {
        // Every line in development, warnings only in production
        logLevel: process.env.NODE_ENV === 'production' ? 'warn' : undefined,
    })
}

Security

Only copy values you would put on a public web page. PublicEnvScript writes every NEXT_PUBLIC_* variable into the HTML of every route under its layout, so makeEnvPublic(['DATABASE_URL']) publishes your database URL.

Related

• Making env public walks through migrating unprefixed config
• PublicEnvScript serves the copies to the browser
• Docker covers standalone builds