Chrome starts measuring Core Web Vitals for single-page apps: what React and Next.js sites need to know

Sites built with React, Vue or other single-page app frameworks often do not load a whole new page when a user clicks a link. Instead, JavaScript swaps the content and changes the URL in place. This is a soft navigation. Users experience a page change, but the browser still treats it as the original page.

As a result, the real-user Core Web Vitals that Chrome collects have mostly reflected the first page load. The Chrome team explains that INP and CLS can be derived from existing APIs, but LCP is only emitted for regular page navigations. SPAs have been missing an important part of the picture.

Chrome built the Soft Navigations API to address this and has tested it through several origin trials. The final trial, announced on 20 April 2026, ran from Chrome 147 to 149, and replaceState now counts as a soft navigation following developer feedback.

According to the CrUX release notes, the September 2026 dataset, published on 13 October, brought the biggest change of the year. It added experimental versions of LCP, INP and CLS that include soft navigations, available in BigQuery, the CrUX API and the History API. CrUX Vis has a toggle to compare the two.

Search Engine Journal reports that the data comes from the Soft Navigations API, on by default since Chrome 151 on 28 July, and that the new fields carry an experimental prefix, such as experimental_largest_contentful_paint_with_softnavs.

The notable figure: counting soft navigations, the share of origins passing Core Web Vitals would be 59.5%, compared with 55.9% without them. Soft navigations tend to be faster than first loads, so many SPAs may have been rated below their real user experience.

For most sites, the impact is small. SEJ reports that about 70% of origins have little or no soft navigation traffic, and 66–75% have soft navigations on under 5% of page views, depending on platform.

Large sites are different. Soft navigations make up more than half of page views on 7.0% of Android origins and 10.6% of desktop origins. Among the top 1,000 sites, the figures rise to 35% on Android and 42% on desktop.

Crucially, stable scores have not changed. Chrome aims to end the experimental phase in May 2027, subject to feedback, and Search Console is expected to adopt the new data after that. SEJ notes no statement on ranking impact, and Chrome cautions that numbers may shift month to month as measurement improves.

This year’s CrUX notes show another trend. The share of origins with good INP fell from 87.1% in January to 85.4% in September, and in the August release the CrUX team said INP was continuing to decline with no definitive cause identified.

LCP and CLS have been fairly stable, and the share passing all three Core Web Vitals has stayed around 55–56% all year. INP, which measures how quickly a page responds to taps and clicks, deserves particular attention, especially on JavaScript-heavy sites.

In our view, many newer Thai business sites are built with Next.js, Nuxt or React and use soft navigations, so this news applies directly. The upside is that if a site was underrated because only the first page was measured, the new data may reflect real experience better.

There is another side. Slow in-app page changes, or layouts that jump while data loads, were previously invisible and will start to show. A site that hid problems behind a fast first load may not look as good as expected.

Most Thai users browse on phones, and mid-range devices have less processing power than the machines development teams test on. INP problems caused by heavy JavaScript are often worse in the field than in the office.

There is no need to rush fixes for scores, since stable values are unchanged. But the experimental period is a good chance to review the data before Search Console adopts it.

If your site runs on WordPress or another system that loads a new page on every click, this news barely affects you. It is still worth checking your INP, since it is the metric that has been slipping across the web this year.

• Open CrUX Vis and toggle between soft-navigation and stable values for your site
• Use the Chrome DevTools Performance panel, which shows soft navigation markers from Chrome 145
• Check in-app page changes for slow loads or layout shifts, especially product and listing pages
• Reduce JavaScript that runs on taps and clicks to improve INP
• Test on mid-range Android phones similar to your customers’ devices