Vercel·Fixdeploybeginner

Works Locally but Vercel Says Environment Variables Are Undefined

Quick Answer

How do I fix Works Locally but Vercel Says Environment Variables Are Undefined?

Env vars added after deployment don't apply to existing deployments. Also, browser-accessible vars need the NEXT_PUBLIC_ prefix. Start with "Add vars and REDEPLOY" before making broader code changes.

Fix signals

What this answers: Why works locally but vercel says environment variables are undefined happens and what to change first.
Fastest move: Add vars and REDEPLOY
Use this page if: App works locally but breaks on Vercel

If this keeps happening

Open the next decision, not just the patch

Use these when the current fix is helpful, but the real answer is a better tool choice, a cleaner workflow layer, or a more trustworthy launch path.

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Firecrawl review

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Quick Fix Summary

Most likely cause	Env vars added after deployment don't apply to existing deployments. Also, browser-accessible vars need the NEXT_PUBLIC_ prefix.
Fastest fix	Add vars and REDEPLOY
Use this page if	App works locally but breaks on Vercel

Exact errors people search for

If one of these matches what you are seeing, you are likely on the right fix page.

Works locally but Vercel says environment variables are undefined
Production build cannot read the env vars I just added
API calls fail on the deployed site because a secret is missing

You're in the right place if...

!App works locally but breaks on Vercel
!Variables are undefined in production
!API calls fail on deployed site

Why this happens

Env vars added after deployment don't apply to existing deployments. Also, browser-accessible vars need the NEXT_PUBLIC_ prefix.

Fix

Add vars and REDEPLOY

After adding env vars, you MUST redeploy. Deployments → three dots → Redeploy.

Check NEXT_PUBLIC_ prefix

Variables used in browser code need NEXT_PUBLIC_ prefix. Server-only variables must NOT have it.

# Browser-accessible (MUST have prefix):
NEXT_PUBLIC_SUPABASE_URL=...
NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=pk_...

# Server-only (NO prefix — keeps it secret):
STRIPE_SECRET_KEY=sk_...
SUPABASE_SERVICE_ROLE_KEY=...

Prevent this next time

Add all environment variables to Vercel BEFORE your first deployment. Saves a redeploy.