Angular "Cannot find module '@angular/core'" in CI

The build tried to resolve an @angular package that is not present in node_modules. In CI this almost always means the install step was skipped, failed silently, or ran in a different job without a shared node_modules.

What this error means

ng build or a tsc step fails with "Cannot find module '@angular/core' or its corresponding type declarations" while the same command works locally.

Error: Cannot find module '@angular/core'
Require stack:
- /home/runner/work/app/app/node_modules/@angular-devkit/build-angular/...

Common causes

Dependencies were never installed on this job

The build ran before npm ci, or a separate CI job did not restore node_modules, so @angular packages are missing.

A partial or failed install left node_modules incomplete

An install that errored midway (network, disk) leaves some @angular packages absent even though the job appeared to continue.

How to fix it

Install with npm ci before the build

1. Ensure a step runs npm ci (using the committed lockfile) before any ng command.
2. If build and install are separate jobs, cache or upload node_modules between them.
3. Fail the job on a non-zero install exit code so a partial install does not continue.

- run: npm ci
- run: npx ng build --configuration production

Verify the package is a real dependency

Confirm @angular/core is listed in package.json dependencies and present in the lockfile, not only installed transiently on a dev machine.

npm ls @angular/core

How to prevent it

• Always run npm ci in the same job that builds.
• Cache node_modules or the npm cache with a lockfile-hashed key.
• Treat a failed install as a hard job failure.

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