Examine source code of SudokuPad Extra Tools

{
  "name": "SudokuPad Extra Tools",
  "manifest_version": 2,
  "version": "2.4",
  "description": "Adds extra tools for SudokuPad (Cracking The Cryptic web app). Pencil mark all candidates, Auto erase pencil marks, Give all possible sum of selected cells based on candidates marks",
  "permissions": [
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://test.crackingthecryptic.com/sudoku/*",
        "https://app.crackingthecryptic.com/sudoku/*",
        "https://sudokupad.app/*"
      ],
      "all_frames": true,
      "js": [
        "ctxmenu.js",
        "content-script.js"
      ],
      "css": [
        "ctxmenu.css"
      ],
      "run_at": "document_end"
    }
  ],
  "web_accessible_resources": [
    "extra-tools.js",
    "ctxmenu.js",
    "ctxmenu.css"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{16ab6681-1d9d-4742-91a1-255388118ec8}",
      "strict_min_version": "48.0"
    }
  }
}