Examine source code of Page Measure Toolkit

{
  "manifest_version": 3,
  "name": "Page Measure Toolkit",
  "short_name": "MeasureX",
  "description": "Lightweight element inspector and distance ruler (hover to inspect, click to measure distances).",
  "version": "2.0.0",
  "default_locale": "en",
  "author": "Valentin Aleksandrov",
  "homepage_url": "https://github.com/valentinaleksandrov/Extension-Ruler",
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "webNavigation",
    "scripting",
    "alarms"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "measurex@valentinaleksandrov.dev",
      "strict_min_version": "109.0"
    }
  },
  "background": {
    "scripts": [
      "src/background/background.js"
    ]
  },
  "action": {
    "default_title": "__MSG_action_toggle_title__",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "commands": {
    "toggle-measure": {
      "suggested_key": {
        "default": "Alt+R"
      },
      "description": "Toggle measurement overlay"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "src/content/preload.js"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "src/lib/box-model.js",
        "src/lib/colors.js",
        "src/lib/dom-helpers.js",
        "src/lib/export.js",
        "src/lib/font-detection.js",
        "src/lib/font-search.js",
        "src/lib/highlight.js",
        "src/lib/layout-inspector.js",
        "src/lib/measurement.js",
        "src/lib/notifications.js",
        "src/lib/panel.js",
        "src/lib/selection.js",
        "src/lib/typography.js",
        "src/lib/utils.js",
        "src/content/overlay.js",
        "src/content/overlay.css"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ]
}