When you use pnpm on a project, you don't want others to accidentally run npm install or yarn. To prevent devs from using other package managers, add the following preinstall script to your package.json:

{
  "scripts": {
    "preinstall": "npx only-allow pnpm"
  }
}

Next time, when someone runs npm install or yarn install, they'll get an error message in the console.

If you use npm v7, this is the command that needs to be added to package.json:

{
  "scripts": {
    "preinstall": "npx -y only-allow pnpm"
  }
}