Chrome Console

Press Cmd + Option + J on a Mac, or Ctrl + Shift + J in Chrome to bring up the Console. The Console is a debugging tool, flagging up errors within Chrome so you can effectively debug and streamline your user experience. In terms of competitor analysis, it also enables you to look behind the scenes at the code, including add-ons, plugins and directories referenced on the page. Think of the console like your x-ray glasses, allowing you to see through the front-end so you can find out what your competitors are up to behind the scenes in terms of their website, analytics and tracking.

https://developer.chrome.com/devtools/docs/console