npm ERR! code E409

What This Error Means

The registry rejected the publish because the version already exists (conflict).

How to Fix It

1. Check which registry npm is using: npm config get registry.
2. If the package is scoped, verify scope registry mapping in .npmrc (example: @your-scope:registry=...).
3. You cannot overwrite an existing version on npm registries. Bump the version and publish again.
4. Confirm what is already published: npm view <pkg> versions --json.

Why It Happens

• The version is already published (most common).
• The package metadata is invalid or violates registry policy.
• You are publishing to the wrong registry or scope.

How to Verify

1. Run npm view <pkg>@<version> and confirm the new version exists after publish.
2. Re-run publish and confirm the registry accepts it.

Manual validation checklist

1. Preview what will be published: npm pack --dry-run (or npm pack and inspect the tarball).
2. Confirm effective registry: npm config get registry.

Common CLI Output

npm ERR! code E409

How npm surfaces this error

1. Registries treat versions as immutable. A version conflict is an expected protection.
2. Invalid package metadata causes publish validation errors.

Prevention Tips

• Automate version bumps as part of release workflow.
• Keep registry routing explicit for scoped packages.
• Validate package contents with npm pack before publishing.

Where This Can Be Triggered

// used by the ping and doctor commands
const npmFetch = require('npm-registry-fetch')
module.exports = async (flatOptions) => {
  const res = await npmFetch('/-/ping', { ...flatOptions, cache: false })
  return res.json().catch(() => ({}))
}