How to fix npm ERR! code E401 npm ERR! 401 Unauthorized in npm

First, check if you're currently logged in to npm:

npm whoami

If this returns an error like ENEEDAUTH or E401, you're not authenticated. If it returns a username, your credentials exist but may be expired or invalid for the specific registry.

Also check which registry npm is configured to use:

npm config get registry

The default public registry is https://registry.npmjs.org/.

Clear your current authentication and log in fresh:

npm logout
npm login

Follow the prompts to enter your npm username, password, and email. For accounts with 2FA enabled, you'll also need to enter a one-time password.

After logging in, verify it worked:

npm whoami

The .npmrc file stores your authentication tokens. Check all locations for stale tokens:

On macOS/Linux:

cat ~/.npmrc

On Windows:

type %USERPROFILE%\.npmrc

Look for lines containing _authToken or _auth. If you see old tokens, remove them:

# Remove the stale token line, or delete the file entirely:
rm ~/.npmrc

Then run npm login again to regenerate valid credentials.

Also check for a project-level .npmrc that might have stale tokens:

cat .npmrc  # In your project directory

If you recently upgraded npm or switched registries, your package-lock.json may contain resolved URLs that no longer match your .npmrc configuration:

rm package-lock.json
npm install

This forces npm to resolve all packages fresh with your current registry and credentials.

Note: If you use a lockfile for reproducible builds, commit the new package-lock.json after it's regenerated.

If your registry configuration is incorrect, reset it to the public npm registry:

npm config set registry https://registry.npmjs.org/

Then try your command again. If you need a private registry, ensure you configure both the registry URL and authentication token correctly.

In some cases, cached authentication data can cause issues:

npm cache clean --force

Then retry your npm command.

For automated environments, use access tokens instead of logging in interactively.

Generate a token on npmjs.com:
1. Go to https://www.npmjs.com/settings/~/tokens
2. Click "Generate New Token"
3. Choose "Granular Access Token" (recommended) or "Classic Token"
4. Set appropriate permissions and expiration

Add the token to your .npmrc:

//registry.npmjs.org/:_authToken=YOUR_TOKEN_HERE

Or use an environment variable (recommended for CI/CD):

//registry.npmjs.org/:_authToken=${NPM_TOKEN}

Then set NPM_TOKEN as a secret in your CI/CD platform.