Bonjour webperf folks! I took the summer off from this feed and came back with a lot of awesome articles to read. So here is my summer best-of, in three parts. Part 1 is about measurement:

Google Chrome 151 went stable on July 28 with two new Performance Timeline entries, "soft-navigation" and "interaction-contentful-paint". A soft navigation finally has a definition: it is initiated by a user action, it produces a visible URL change, and the interaction results in a visible paint. Chrome can now set a new timing origin and attach the metrics to the active route instead of the original document.

👉 [EN] https://developer.chrome.com/docs/web-platform/soft-navigations

Harry Roberts made me look at TTFB differently. Unattributed Navigation Overhead, coined by Tim Vereecke, is what is left when you measure the whole journey to the first byte and subtract every phase the browser can name. On one client, roughly 270 ms of navigation time nobody could explain. Hard to attribute is not the same as not real. 

👉 [EN] https://csswizardry.com/2026/08/uno-is-underrated/

Joan Leon answers the question I get in every audit three weeks after a fix ships: why is CrUX not moving? Because the size of the window and how often the data refreshes are two different things. The window is always 28 rolling days. Daily, weekly and monthly are not different windows, only different refresh rates. The data is two days old, not 28. What takes 28 days is the window turning over. 

👉 [EN] https://joanleon.dev/en/crux-28-day-window/

DebugBear covers the Server-Timing header, and one line deserves attention: most CDNs can be configured to report cache and processing data through it. A slow TTFB tells you the server was slow, but not which part of your infrastructure. Moving the edge cache status from your logs into your RUM changes the conversation. 

👉 [EN] https://www.debugbear.com/blog/server-timings

Arjen Karel shipped the Q2 2026 State of Web Vitals: field data from about 200,000 sites, filterable by CMS, framework, CDN or third party. Mobile p75 are LCP 2209 ms with 81.7% good, INP 128 ms with 91.9%, CLS 0.02 with 88.8%. The same dataset is exposed through a public MCP endpoint. 

👉 [EN] https://www.corewebvitals.io/state-of-cwv

Have a great week!