Examine source code of 1337coder

{
  "manifest_version": 2,
  "name": "1337coder",
  "version": "0.3",
  "description": "Parses example input & answers during leetcode competition and pastes it into Custom Testcases and (Un)Expected answer",
  "icons": {
    "48": "icons/1337-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.leetcode.com/contest/*"
      ],
      "js": [
        "1337coder.js"
      ]
    }
  ]
}