manifest.json

{
  "name": "Awesome extension name",
  "version": "0.1",
  "manifest_version": 2,
  "description": "Blah blah blah..",
  "icons": {"48": "icon48.png"},
  "permissions": [
    "tabs", "cookies", "*://*/*"
  ],
  "content_scripts": [
    {
      "matches": ["http://localhost:3000/*"],
      "js": ["jquery.min.js", "content.js"],
      "run_at": "document_end"
    }
  ],
  "background": {
    "scripts": ["background.js"]
  }
}