How to fix npm ERR! code EDUPLICATEWORKSPACE npm ERR! must not have multiple workspaces with the same name in npm

First, identify which workspaces have duplicate names. You can use grep to extract all workspace names:

find . -path ./node_modules -prune -o -name 'package.json' -type f -exec grep -H '"name"' {} \;

On Windows PowerShell:

Get-ChildItem -Path . -Filter 'package.json' -Recurse | Select-String '"name"'

This will show all package.json files with their name fields. Look for any names that appear more than once.

Review the workspaces field in your root package.json to understand which directories are included:

{
  "name": "my-monorepo",
  "workspaces": [
    "packages/*",
    "apps/*",
    "services/*"
  ]
}

Note all glob patterns, as they may be catching duplicate packages.

Update the name field in each duplicate package.json to be unique. Use a consistent naming convention, preferably with scoping:

{
  "name": "@mycompany/auth",
  "version": "1.0.0"
}

For example, if you have packages/api and services/api both with name "api", rename them to:
- packages/api/package.json: "name": "@mycompany/api-packages"
- services/api/package.json: "name": "@mycompany/api-services"

After updating all duplicate package names, clean your npm cache and reinstall:

rm -rf node_modules package-lock.json
npm cache clean --force
npm install

This ensures npm re-validates your workspace configuration with the corrected names.

After renaming, update any cross-workspace dependencies in your package.json files to reference the new names:

{
  "name": "@mycompany/app",
  "dependencies": {
    "@mycompany/api-services": "workspace:*"
  }
}

The workspace:* protocol ensures the dependency points to the local workspace version rather than npm registry.