How do I add comments to package.json for npm install?

I've got a simple package.json file and I want to add a comment. Is there a way to do this, or are there any hacks to make this work?

{
  "name": "My Project",
  "version": "0.0.1",
  "private": true,
  "dependencies": {
    "express": "3.x",
    "mongoose": "3.x"
  },
  "devDependencies" :  {
    "should": "*"
    /* "mocha": "*" not needed as should be globally installed */
  }
}

The example comment above doesn't work as npm breaks. I've also tried // style comments.

This has recently been discussed on the Node.js mailing list.

According to Isaac Schlueter who created npm:

... the "//" key will never be used by npm for any purpose, and is reserved for comments ... If you want to use a multiple line comment, you can use either an array, or multiple "//" keys.

When using your usual tools (npm, yarn, etc.), multiple "//" keys will be removed. This survives:

{ "//": [
  "first line",
  "second line" ] }

This will not survive:

{ "//": "this is the first line of a comment",
  "//": "this is the second line of the comment" }

One must be aware that "//" can only be used at the root of the package.json object. For example

{ 
  "//": "comment!", 
  "dependencies": {...}
} 

is valid but

{ 
  "dependencies": { 
     "//": "comment?" 
  }
}

is invalid.

-- @david_p comment