Examine source code of Word Counter

{
  "version": "4.0.0",
  "manifest_version": 2,
  "name": "Word Counter",
  "short_name": "wordcount",
  "permissions": [
    "storage",
    "contextMenus"
  ],
  "background": {
    "page": "lib/chrome/background.html"
  },
  "homepage_url": "https://greatseotools.net",
  "description": "Word Counter allows you to count the number of selected words and characters in a single click.",
  "content_scripts": [
    {
      "all_frames": false,
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "data/content_script/inject.js"
      ]
    }
  ],
  "icons": {
    "16": "data/icons/icon-16.png",
    "48": "data/icons/icon-48.png",
    "128": "data/icons/icon-128.png"
  }
}