Cannot find module

Node tried to load a package or file that isn’t where the code says it is, usually because it was never installed or the path is wrong.

Terminal
Error: Cannot find module 'express' Require stack: - /Users/me/my-app/server.js

Also appears as

  • Error [ERR_MODULE_NOT_FOUND]: Cannot find package 'express' imported from /Users/me/my-app/server.js
  • Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/Users/me/my-app/src/utils' imported from /Users/me/my-app/src/index.js Did you mean to import "./utils.js"?

Prompt to fix it

Running the app fails with "Error: Cannot find module" (code MODULE_NOT_FOUND). Read the full error and the Require stack, and tell me whether the missing name is a package or a file in this project. If it’s a package, add it with npm install, under dependencies if the server needs it at runtime. If it’s a file, fix the path and match the file’s exact letter case, since the production server is case-sensitive. Check that compiled output doesn’t still contain @/ path aliases. Don’t install anything globally to work around it.

Paste into Layerwise or any AI coding tool.

What it means

Node prints this when a require() or import names something it can’t find. For a bare name like express, it searches the node_modules folder next to the file, then each parent folder’s. For a path like ./utils, it looks for that exact file. Require stack lists the file that asked, and code: 'MODULE_NOT_FOUND', or ERR_MODULE_NOT_FOUND for files that use import, marks it as a failed lookup.

Most of the time the package isn’t installed where the code runs. AI tools sometimes write import express from 'express' without adding express to package.json, and a fresh clone or exported project has no node_modules until you run npm install. On servers, packages listed under devDependencies are often left out of production installs.

The trap is a path that only works on your machine. macOS and Windows treat ./Utils and ./utils as the same file, and Linux servers don’t, so a letter-case mismatch passes locally and fails on deploy. Files that use import are stricter too: Node needs the full file name with .js, and its hint Did you mean to import "./utils.js"? points right at the fix.

Common causes

  • The package was never installed: the project was cloned or exported without npm install, or the code imports a package that isn’t listed in package.json.
  • The package is in devDependencies, and the server’s install skips those with npm ci --omit=dev or NODE_ENV=production.
  • The path is wrong, or its letter case differs from the file on disk, which macOS and Windows forgive and Linux servers don’t.
  • The server runs compiled TypeScript that still imports aliases like @/lib/db, which tsc doesn’t rewrite, or ES module imports without the .js extension.

How to fix it

  1. Read the name in quotes. A bare name like express is a package; a name starting with ./, ../, or @/ is a file in your project.
  2. For a package, run npm install express in the folder that holds package.json, and check it lands under dependencies if the server needs it at runtime.
  3. For a file, confirm it exists at that path with the exact same letter case. Make case-only renames with git mv so git records them.
  4. In files that use import, write the full file name, such as ./utils.js. For compiled TypeScript, replace @/ aliases with relative paths, or run the code with a tool like tsx that resolves them.
  5. If the package is installed and the path is right, run npm ci to rebuild node_modules from the lockfile.

Example fix

# A bare name like 'express' is a package: install it next to package.json.
npm install express

# Rebuild node_modules exactly from the lockfile if it looks broken.
npm ci

# Git on macOS and Windows misses case-only renames unless you use git mv.
git mv src/Utils.js src/utils.js

Related errors

All errors
src/App.tsx:3:20 - error TS2307: Cannot find module '@/components/Header' or its corresponding type declarations.

Cannot find module or its corresponding type declarations

TypeScript couldn’t match an import to a file or package it understands, so the build fails even when the app runs fine in the browser.

./src/app/page.tsx:2:1 Module not found: Can't resolve '@/components/Header'

Module not found: Can't resolve

The bundler followed an import to a file or package that doesn’t exist under that name, so it couldn’t build the page.

SyntaxError: Cannot use import statement outside a module

Cannot use import statement outside a module

A file written with import syntax was loaded as an old-style script or CommonJS file, so loading stopped at the first import line.

> my-app@0.0.0 dev > vite sh: vite: command not found

vite: command not found

The shell couldn’t find the vite program, almost always because the project’s packages aren’t installed or the command ran in the wrong folder.

Build with an agent that checks its work

The Layerwise agent clicks through the live preview and reads the console, so it catches errors before you do.

DownloadRead the docs