The npm E401 error occurs when your authentication token or credentials for a private npm registry have expired, been invalidated, or are misconfigured in your .npmrc file. This prevents npm install from accessing private packages you have permission to use.
Fixes E401
npm whoaminpm whoaminpm ERR! code E401npm ERR! Registry authentication data invalid
npm returns a 401 Unauthorized error when it tries to authenticate with a registry and the credentials fail validation. This usually means your authentication token has expired, your password was reset, your .npmrc contains stale credentials, or the token was revoked.
Check whether npm recognizes you as logged in:
npm whoamiIf this returns 'unauthenticated', you need to log in.
Locate your .npmrc file:
cat ~/.npmrcIf you see an old authToken, it may be expired.
Log in again to refresh your credentials:
npm loginThis will overwrite the old token in your .npmrc with a fresh one.
If using Azure DevOps Artifacts:
1. Go to Azure DevOps → Personal Access Tokens
2. Regenerate expired tokens
3. Run:
vsts-npm-auth -config .npmrcIf npm v7+ is in use, package-lock.json may contain cached registry credentials:
rm package-lock.json
npm installAs a last resort, delete and recreate your .npmrc:
rm ~/.npmrc
npm loginThe npm E401 error has several nuances: Package-lock.json can cache resolved URLs with embedded credentials; upgrading npm v6→v7 sometimes breaks private registry compatibility if the protocol doesn't match exactly. Azure DevOps uses personal access tokens with expiration dates—these must be renewed separately using vsts-npm-auth.