# npm "Cannot find module" After --omit=dev - Build Tool Stripped in CI

> Fix builds that break after `npm ci --omit=dev` in CI - a compiler or bundler needed at build time lives in devDependencies and gets stripped, so the build step cannot find it.

Source: https://latchkey.dev/learn/node-js/npm-ci-omit-dev-missing-build-dep  
Updated: 2026-06-25

A production install (`--omit=dev` or `NODE_ENV=production`) drops devDependencies. If your build step needs a tool that lives there - TypeScript, a bundler, a plugin - the build then fails to find it.

## Diagnose it: reproduce the CI install locally

Install failures are usually environment drift rather than a broken lockfile: a different package-manager major, a different Node version, or a cache that is being restored from a run with different inputs. Reproduce the CI conditions before changing the lockfile, because regenerating it hides the real cause.

```Terminal
# match the runner exactly, then install from a clean slate
node --version && npm --version
rm -rf node_modules
npm ci --foreground-scripts

# if that succeeds locally but fails in CI, the difference is the cache
# or the package-manager version, not your lockfile
```

> Pin the package manager with Corepack (`"packageManager"` in package.json) so the runner and every developer machine resolve the same version. Version skew is the single most common source of lockfile errors that only appear in CI.

## Verify the fix survives a cold cache

A green run immediately after a fix often proves nothing, because it restored a cache written before the change. Force a cold install once to confirm the fix is real.

```.github/workflows/ci.yml
# temporarily bust the cache key to prove the fix on a cold runner
- uses: actions/setup-node@v4
  with:
    node-version: 22
    cache: npm
    cache-dependency-path: package-lock.json
# then bump this suffix once, run, and remove it
#   key: ${{ runner.os }}-node-${{ hashFiles('package-lock.json') }}-v2
```

## FAQ

### What causes npm "Cannot find module" after --omit=dev?

There are 2 common causes: build tooling is in devdependencies but the build runs after a prod install and node_env=production implicitly omits dev deps. Compilers and bundlers are devDependencies by convention.

### How do I fix npm "Cannot find module" after --omit=dev?

There are 2 fixes depending on which cause you have: install dev deps for the build, prune after and split build and runtime installs. Work through them in order, since the first is the most common.

### What does npm "Cannot find module" after --omit=dev actually mean?

Install succeeds, but the build step crashes with Cannot find module for a build tool (e.g.

### How do I stop npm "Cannot find module" after --omit=dev happening again?

Build with all deps; prune to production afterward. The prevention section lists 3 changes that keep it from recurring.

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Latchkey runs CI/CD that repairs its own failures. Agent entry points: https://latchkey.dev/agent.txt, https://latchkey.dev/openapi.json, https://latchkey.dev/llms.txt