How to Fix Vercel Deployment Errors

You deploy to Vercel and get a wall of red errors. Everything works perfectly on localhost.

This article covers the most common Vercel deployment errors organized by error type. Find your error message, understand the cause, and fix it fast.

Pre-Deploy Checklist

Run these three commands locally before every push. They catch most build errors before they reach Vercel.

npx tsc --noEmit        # TypeScript type checking
npm run lint             # ESLint check
npm run build            # Production build

"Works in dev" and "passes build" are different things. Dev mode treats TypeScript errors as warnings. Build mode treats them as fatal errors.

Common oversights:

• Never running npm run build locally before pushing
• Environment variables available in dev but missing in build
• TypeScript strict mode only activating in CI

Build Errors and How to Fix Them

Module not found

Error: Module not found: Can't resolve './Components/Header'

Cause: File name casing mismatch. macOS and Windows are case-insensitive, but Vercel (Linux) is case-sensitive.

Locally, import Header from './Components/Header' works even if the file is components/Header.tsx. On Vercel, it fails.

Fix:

# Enable case-sensitive git tracking (prevents future issues)
git config core.ignorecase false

Match your import paths exactly to the actual file names on disk.

Dependency resolution errors

npm ERR! Could not resolve dependency

Cause: package-lock.json or Node.js version mismatch between local and Vercel.

Fix:

1. Vercel Dashboard → Settings → General → Node.js Version — match it to your local version
2. Delete package-lock.json, run npm install, and recommit

Corrupted build cache

Build logs show bizarre errors and nothing has changed in your code.

Fix: Vercel Dashboard → Deployments → click "..." on the failed deploy → Redeploy without cache.

Works Locally, Fails on Vercel

The most frustrating pattern. The cause is almost always one of these three.

1. Writing to the file system

Error: EROFS: read-only file system, open '/var/task/data.json'

Serverless Function file systems are read-only. fs.writeFileSync works on your local Node.js server but fails on Vercel.

Fix: Use /tmp for temporary writes (500 MB limit). For persistent storage, use a database or object storage.

import { writeFileSync } from "fs";
import { join } from "path";

// NG: Read-only on Vercel
writeFileSync("./data.json", JSON.stringify(data));

// OK: /tmp is writable
writeFileSync(join("/tmp", "data.json"), JSON.stringify(data));

2. Missing environment variables

Environment variables in .env.local don't automatically sync to Vercel.

Fix: Vercel Dashboard → Settings → Environment Variables — add them manually. Make sure to check all three environments: Development, Preview, and Production.

3. Node.js version mismatch

Your local environment runs Node 22 while Vercel defaults to a different version, causing ES module resolution or API compatibility differences.

Fix: Vercel Dashboard → Settings → General → Node.js Version — match your local version. Or add a .node-version file to your project root.

Runtime Errors (500, Timeouts)

Build succeeds, but the site returns 500 or specific pages break after deployment.

Serverless Function has crashed

FUNCTION_INVOCATION_FAILED

Common causes:

• Uncaught exceptions (missing try/catch)
• Out of memory (Hobby plan: 2 GB limit)
• Environment variables missing, causing DB/API connection failures

Fix: Vercel Dashboard → Logs — check runtime logs for error details.

FUNCTION_INVOCATION_TIMEOUT

Task timed out after 10 seconds

Cause: With Fluid Compute disabled, Hobby plan's default timeout is 10 seconds. Fluid Compute is now enabled by default, extending the default to 300 seconds. But older projects or manually disabled settings may still have the 10-second limit.

FUNCTION_PAYLOAD_TOO_LARGE

FUNCTION_PAYLOAD_TOO_LARGE

The request body exceeds 4.5 MB. This hits file uploads or large JSON payloads.

Fix: For large files, use presigned URLs to upload directly to S3 or R2 instead of going through the serverless function.

When it's not your code: Vercel outages

Sometimes the error has nothing to do with your code.

On March 2, 2026, a Dubai region (dxb1) infrastructure failure blocked deployments for all Vercel users worldwide for 10+ hours. The cause was Vercel's architecture: Middleware deploys to all regions, so a single region failure prevented any Middleware-using project from deploying globally.

When deployments suddenly fail without any code changes:

1. Check vercel-status.com first
2. If it's a Vercel outage, there's nothing to do but wait
3. After resolution, use Redeploy without cache

Environment Variable Gotchas

Environment variables are the most confusing part of Vercel deployments.

build-time vs runtime

Next.js has two types of environment variables.

Common mistakes

Adding quotes in the dashboard:

# Wrong (in Vercel dashboard)
NEXT_PUBLIC_API_URL="https://api.example.com"

# Correct
NEXT_PUBLIC_API_URL=https://api.example.com

In Vercel's environment variable settings, quotes are not needed. Adding them makes the quotes part of the value.

Not checking Preview environment:

When adding environment variables, there are three checkboxes: Production, Preview, and Development. If Preview is unchecked, preview deployments (automatic deploys per PR) won't have access to the variable.

Know Your Plan Limits

Sometimes the error is just a plan limitation.

If you're hitting FUNCTION_INVOCATION_TIMEOUT frequently on Hobby, the 10-second limit is likely the cause. Enable Fluid Compute or optimize the function.

Frequently Asked Questions

Why does my build pass locally but fail on Vercel?

The three most common causes are file name casing (Linux is case-sensitive, macOS/Windows aren't), missing environment variables (.env.local doesn't sync to Vercel), and Node.js version differences. Run git config core.ignorecase false and match your Node.js version in Vercel Dashboard → Settings → General.

How do I check if Vercel itself is having issues?

Go to vercel-status.com. If there's an ongoing incident, your deployment failure may not be related to your code at all. Wait for resolution and then use "Redeploy without cache."

What's the difference between NEXT_PUBLIC_ and regular environment variables?

NEXT_PUBLIC_ variables are inlined into JavaScript at build time — changing them in the dashboard requires a rebuild. Regular server-side variables (without the prefix) are read at request time and take effect immediately after updating in the dashboard.

How do I fix FUNCTION_INVOCATION_TIMEOUT on the Hobby plan?

First check if Fluid Compute is enabled (Vercel Dashboard → Settings → Functions). With Fluid Compute, the timeout extends to 300 seconds. If it's already enabled, optimize your function — reduce external API calls, add caching, or move heavy processing to a background job.

Can I write files on Vercel?

Only to the /tmp directory, with a 500 MB limit. The rest of the file system is read-only in serverless functions. For persistent storage, use a database, S3, or Cloudflare R2.

Why do my environment variables work in Production but not in Preview?

When adding environment variables in the Vercel dashboard, there are three checkboxes: Production, Preview, and Development. If Preview isn't checked, PR preview deployments won't have access to that variable.

How do I clear Vercel's build cache?

Go to Vercel Dashboard → Deployments → click "..." on the deployment → select "Redeploy without cache." This is especially important after changing environment variables or updating dependencies.

Wrapping Up

90% of "works locally, fails on Vercel" comes down to three things: case sensitivity, environment variables, and file system access. Remember these three and you'll solve most deployment errors quickly.

To prevent unexpected billing from Vercel's usage-based pricing, check out the Spend Management Guide.

Related articles:

• Vercel vs Netlify vs Cloudflare Pages: The Real Differences
• Vercel Pro Billing Surprise? Check Your Spend Management Now
• Why You Should Migrate from WordPress to Vercel
• Why Your Next.js SSR Isn't Working — App Router Pitfalls