Where does frontend time data come from?

Frontend time data is derived from the W3C navigation timings, which is part of the browser's performance metrics. The W3C navigation timings API provides a standardized way to measure and report the time taken for various phases of page loading. This includes important events such as redirects, DNS resolution, connection setup, and the actual time taken to fetch the document.

By collecting this data, developers and performance engineers gain insights into how long it takes for a web page to load from the user's perspective and can identify bottlenecks in the loading process. This information is critical for optimizing user experience, as it helps in pinpointing areas where improvements can be made in how quickly the content is available to the user.

In contrast, the other options do not directly provide frontend time data in the same standardized, holistic manner as the W3C navigation timings API does. CSS parsing results or JavaScript execution logs might furnish detailed timing related to specific resources or scripts, but they do not encompass the full scope of what affects the overall frontend loading time. Performance monitoring tools can provide analytics and visualizations, but they aggregate data from various sources rather than being the original source themselves.