The Future of Web Performance Metrics: What's After Core Web Vitals?

Core Web Vitals have already evolved once — FID was replaced by INP in March 2024. Google has signaled that the metrics will continue to evolve. Here's what's coming next and how to prepare.

The Evolution So Far

Year	Change
2020	Core Web Vitals introduced (LCP, FID, CLS)
2021	CWV becomes a ranking signal
2024	INP replaces FID
2025	CLS measurement refined (windowed approach)
2026+	New metrics under development

Long Animation Frames (LoAF)

The Long Animation Frames API is the successor to the Long Tasks API. While Long Tasks only told you "something took too long," LoAF tells you exactly what happened:

• Which scripts ran and for how long
• Whether rendering work was included
• The total frame duration
• What caused the frame to be long

Why LoAF Matters

LoAF provides the attribution data needed to actually fix INP issues. Instead of knowing "interaction took 400ms," you can see "300ms was spent in vendor-analytics.js processing a click handler."

const observer = new PerformanceObserver((list) => {
  for (const entry of list.getEntries()) {
    console.log('Long frame:', entry.duration, 'ms');
    for (const script of entry.scripts) {
      console.log('  Script:', script.sourceURL, script.duration, 'ms');
    }
  }
});
observer.observe({ type: 'long-animation-frame', buffered: true });

Smooth Responsiveness Metrics

Google is exploring metrics that go beyond INP to capture the overall smoothness of a page:

Animation Smoothness

Measuring whether CSS animations and transitions run at 60fps. Dropped frames during scroll, transitions, or animations feel janky even if INP is good.

Scroll Responsiveness

How quickly the page responds to scroll input. Currently not captured by any Core Web Vital, but users notice scroll jank immediately.

Multi-Interaction Patterns

INP reports the worst single interaction. Future metrics might evaluate the overall interaction pattern — are most interactions smooth with one outlier, or is everything slow?

Improved CLS Measurement

CLS measurement has already evolved from "entire page lifecycle" to a "windowed" approach. Future improvements may include:

• Navigation CLS — measuring shifts during soft navigations in SPAs
• User-initiated vs. unexpected shifts — distinguishing between shifts the user caused (clicking an accordion) and unexpected shifts
• Scroll-triggered CLS — handling shifts that occur during scroll (currently excluded)

Soft Navigation Metrics

Single Page Applications (SPAs) only get Core Web Vitals for the initial page load. Client-side navigations (clicking a link in a React app) aren't measured.

Google is developing soft navigation detection to measure:

• LCP for client-side navigations
• CLS during route transitions
• INP throughout the entire session

This would level the playing field between SPAs and multi-page sites.

Resource Loading Metrics

Potential new metrics focused on resource efficiency:

• Total page weight — penalizing unnecessarily large pages
• Unused resource ratio — measuring how much downloaded code is actually used
• Third-party impact — isolating the performance cost of third-party scripts

What Google Has Said

Google's Chrome team has made several public statements:

1. Core Web Vitals will continue to evolve based on user research
2. Changes will be announced well in advance (6+ months)
3. The focus will shift toward responsiveness and smoothness
4. SPAs will get better measurement through soft navigation support
5. Attribution (understanding the cause of poor metrics) is a priority

How to Prepare

1. Build a Performance Culture

Don't just optimize for current metrics. Build systems and processes that prioritize performance:

• Performance budgets in CI/CD
• Regular audits and reviews
• Developer training on performance best practices

2. Monitor Broadly

Track metrics beyond just Core Web Vitals:

• Long Animation Frames
• JavaScript execution time
• Resource sizes and counts
• Custom user timing marks

3. Focus on User Experience

Metrics are proxies for user experience. If you optimize for real user satisfaction, you'll naturally perform well on whatever metrics Google introduces next.

4. Reduce JavaScript Dependency

The common thread across all performance improvements is less JavaScript:

• Use the platform (HTML, CSS) instead of JS when possible
• Server-render content
• Lazy-load aggressively
• Choose lighter frameworks

5. Automate Monitoring

New metrics will be added to tools like Lighthouse and CrUX. Having automated monitoring in place means you'll see new metric data as soon as it's available.

Stay Ahead of the Curve

BadPageSpeed tracks all Lighthouse metrics and updates as new metrics are added. Stay ahead of Google's evolving standards.

Start future-proof monitoring →