Update: Check out headless-devtools, a library for automating DevTools actions from code by leveraging the DevTools Protocol
Chrome DevTools is the go-to analysis tool for understanding what's going on under-the-covers of your app and conducting perf-audits. As you are interacting with the site like a real user would, you can use DevTools to drill-down to every tiny detail about the page.
... read the whole story at blog.cowchimp.com.
This is great for manual analysis. But if your goal is to monitor web performance over time, you might find that tools in that space are not as powerful. Automated synthetic monitoring services don't expose nearly as much information as there is in DevTools, and for the most part the only type of user interaction they emulate is waiting for the page to load.