What causes "Vercel Environment Variables Not Working (Undefined)"?

Variable added after the last deployment (no redeploy) Variable scoped to Production but you are on a Preview deployment, or vice versa Branch-specific Preview variable overriding the general one NEXT_PUBLIC_ variable missing at build time, so it is inlined as undefined Monorepo/Turborepo not passing variables to the build task Edge runtime limit of 5 KB per variable (64 KB total per deployment)

How do I fix "Vercel Environment Variables Not Working (Undefined)"?

1. Redeploy after changing variables: Settings > Environment Variables: confirm the variable is saved Go to Deployments, open the latest deployment and click Redeploy Changes never apply to existing deployments 2. Check the environment scope: Edit the variable and confirm Production, Preview and/or Development are ticked For preview branches, check for a branch-specific value overriding it 3. Fix NEXT_PUBLIC_ variables: Make sure the variable exists before the build runs Use the exact NEXT_PUBLIC_ prefix Redeploy without build cache if the old value persists 4. Sync local development: Run vercel env pull to write Development variables to .env Or use vercel dev, which loads them automatically 5. Monorepos: Declare the variables in turbo.json env/globalEnv for the build task Confirm the project's Root Directory is the app that reads the variable

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Vercel Environment Variables Not Working (Undefined)

Ongoing Web, Vercel CLI Updated October 21, 2026

Quick answer

Vercel only applies environment variable changes to new deployments, and only to the environments you ticked. Redeploy after every change, check the Production/Preview scope, and remember NEXT_PUBLIC_ variables are baked in at build time.

Most likely fix: Redeploy after changing variables.

Symptoms

process.env.MY_VAR is undefined in production or preview, a NEXT_PUBLIC_ value is missing in the browser, or the build fails because a variable is undefined.

Why it happens

Variable added after the last deployment (no redeploy)
Variable scoped to Production but you are on a Preview deployment, or vice versa
Branch-specific Preview variable overriding the general one
NEXT_PUBLIC_ variable missing at build time, so it is inlined as undefined
Monorepo/Turborepo not passing variables to the build task
Edge runtime limit of 5 KB per variable (64 KB total per deployment)

How to fix it

Try these in order — the most common fix is first.

1. Redeploy after changing variables
1. Settings > Environment Variables: confirm the variable is saved
2. Go to Deployments, open the latest deployment and click Redeploy
3. Changes never apply to existing deployments
2. Check the environment scope
1. Edit the variable and confirm Production, Preview and/or Development are ticked
2. For preview branches, check for a branch-specific value overriding it
3. Fix NEXT_PUBLIC_ variables
1. Make sure the variable exists before the build runs
2. Use the exact NEXT_PUBLIC_ prefix
3. Redeploy without build cache if the old value persists
4. Sync local development
1. Run vercel env pull to write Development variables to .env
2. Or use vercel dev, which loads them automatically
5. Monorepos
1. Declare the variables in turbo.json env/globalEnv for the build task
2. Confirm the project's Root Directory is the app that reads the variable

This guide also covers

vercel environment variables not working
vercel env undefined
next_public env undefined vercel
vercel env variables not updating
vercel env pull

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