Chapter 16. A Practical Guide to the Navigation Timing API

Buddy Brewer

Navigation Timing ( is an API from the W3C’s Web Performance Working Group ( that exposes data about the performance of your web pages. Navigation Timing is a major new development because it enables you to collect fine-grained performance metrics from real users, including events that happen before Javascript-based trackers have a chance to load. This gives us the ability to directly measure things like DNS resolution, connection latency, and time to first byte from inside the browsers of real users.

Why You Should Care

I spent the first eight years of my career building synthetic monitoring products but I now believe real user monitoring should be your preferred source of “The Truth” when it comes to understanding the performance of your site. That doesn’t mean you should throw away your synthetic monitoring, but today I view it as a useful complement to real user monitoring rather than a complete performance solution in itself.

Real user monitoring is critical because it provides the most accurate portrayal of the true experience across the browsers, locations, and networks your users are on. It is the only way to realistically measure how your caching decisions impact the user experience. Measuring real people (with real personalities and real credit cards) also gives you an opportunity to collect ...

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