DevPilot
web-development·September 21, 2026·2 min read

Deploying a Next.js App to Vercel with Environment Variables

A practical guide to deploying Next.js applications on Vercel with proper environment configuration.

deploymentvercelnextjsenvironment-variables

Deploying a Next.js App to Vercel with Environment Variables

Vercel integrates tightly with Next.js but requires careful environment setup.

Problem

Missing environment variables cause build or runtime errors on Vercel that don't appear locally.

Working approach

  • Define variables in .env.local for development.
  • Add production variables in the Vercel project settings.
  • Reference variables using process.env only where needed.

See troubleshooting/databases/database-connection-production for diagnosing database connection failures that share the same root cause: differences between local persistent servers and serverless execution environments (see deployment environment variables).

Prerequisites

  • A Next.js project (App Router or Pages Router) deployed on Vercel.
  • Access to the Vercel project settings (Project → Settings → Environment Variables).
  • A .env.local file for local development (not committed to Git).

Common failure modes

  • Missing .env.local locally: build succeeds locally but fails on Vercel because production variables are not defined.
  • Variables defined in .env.local but not added to Vercel: build passes locally but fails at runtime (variables are undefined in production).
  • Variables with the wrong prefix: Vercel requires variables used in the browser to be prefixed with NEXT_PUBLIC_; server-only variables should not use that prefix.
  • Variables containing special characters not escaped in Vercel settings.

Verification

  1. Check .env.local exists locally and contains required variables.
  2. Confirm the same variables (with identical keys) exist in Vercel project settings.
  3. Confirm process.env.VAR_NAME is used correctly (not hardcoded values).
  4. Deploy a preview branch; open Vercel function logs; confirm no undefined errors.
  5. Confirm variables are not accidentally included in client-side bundles (use server-only variables without NEXT_PUBLIC_ for secrets; only expose what is required in the browser).

Run a preview deployment and check the Vercel function logs for missing variable errors.

Related articles

  • See web-development/react/react-server-actions for a concrete server mutation pattern that relies on the environment variables configured here.
  • See troubleshooting/databases/database-connection-production for diagnosing database connection differences between local persistent servers and serverless execution environments (same root cause as missing environment variables).