npm E404 Not Found in CI - Fix Missing Package Errors

E404 means the registry has no package, version, or scope matching your request. It is a lookup failure, so retrying the same request will keep returning 404.

What this error means

npm install fails with code E404 and 404 Not Found for a specific package. The name may be misspelled, the version may not exist, or a scoped package may be resolved against the wrong registry.

npm

npm ERR! code E404
npm ERR! 404 Not Found - GET https://registry.npmjs.org/@acme%2fui
npm ERR! 404 '@acme/ui@^2.0.0' is not in this registry.

Common causes

A misspelled or unpublished package or version

The name or requested version does not exist on the registry being queried.

A scoped package mapped to the wrong registry

A private scope is queried against the public registry, which has never heard of it, returning 404.

How to fix it

Verify the name and version

Check the package exists with npm view <pkg>.
Correct the name or version range in package.json.

Terminal

npm view @acme/ui versions

Point the scope at the right registry

Add a scope-to-registry mapping in .npmrc for private scopes.
Reinstall so npm queries the correct registry.

.npmrc

@acme:registry=https://registry.acme.internal/

How to prevent it

Pin versions that exist, configure scoped-registry mappings, and validate new dependency names before merge so a clean CI install never hits a 404.