Professional websites with complex UI features provide real world examples for developers to learn from. Yet despite the availability of source code, it is still difficult to understand how these features are implemented. Existing tools such as the Chrome Developer Tools and Firebug offer debugging and inspection, but reverse engineering is still a time consuming task. We thus present Unravel, an extension of the Chrome Developer Tools for quickly tracking and visualizing HTML changes, JavaScript method calls, and JavaScript libraries. Unravel injects an observation agent into websites to monitor DOM interactions in real-time without functional interference or external dependencies. To manage potentially large observations of events, the Unravel UI provides affordances to reduce, sort, and scope observations. Testing Unravel with 13 web developers on 5 large-scale websites, we found a 53% decrease in time to discovering the first key source behind a UI feature and a 32% decrease in time to understanding how to fully recreate a feature.