Examine source code of Slack Direct

{
  "manifest_version": 2,
  "name": "Slack Direct",
  "version": "0.4",
  "description": "Rewrite links within Slack to avoid slack-redir.net",
  "icons": {
    "96": "icon-96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.slack.com/*"
      ],
      "js": [
        "slack-direct.js"
      ]
    }
  ]
}