Examine source code of WriteRoom

{
  "name": "WriteRoom",
  "version": "1.0.0",
  "description": "Substack Management Tool",
  "manifest_version": 2,
  "icons": {
    "16": "16.png",
    "32": "32.png",
    "128": "128.png"
  },
  "content_scripts": [
    {
      "js": [
        "assets/contentScript.js"
      ],
      "matches": [
        "https://*.substack.com/*"
      ],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": [
      "assets/background.js"
    ],
    "persistent": false
  },
  "host_permissions": [
    "http://localhost:3000/*",
    "https://*.substack.com/*"
  ],
  "externally_connectable": {
    "matches": [
      "http://localhost:*/*",
      "https://*.writeroom.co/*"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3b77e216-8643-4d9e-98f7-e5cd9ccc7424}"
    }
  }
}