Examine source code of Skribblio Snapper

{
  "manifest_version": 2,
  "name": "Scribblio Snapper",
  "version": "1.0",
  "description": "Takes a screenshot of your drawings at the end of each round",
  "icons": {
    "48": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://skribbl.io/*"
      ],
      "js": [
        "snapper.js"
      ]
    }
  ]
}