Are Core Web Vitals Really Trustworthy in Measuring Your Site's Actual Performance?

Why Does Google Acknowledge the Imperfections of Its Own Metrics?

This statement breaks from Google's usual communication. Publicly admitting that Core Web Vitals do not always reflect the on-the-ground reality is a rare concession. It suggests that the search engine is aware of false positives — sites penalized despite good actual performance — and false negatives — poorly rated sites where users experience no issues.

This admission comes in a context where SEO practitioners are multiplying contradictory observations. Sites with a LCP under 2.5 seconds that fall behind competitors showing 4 seconds. Mobile-friendly pages rated "needs improvement" while objectively degraded experiences turn green. The gap between lab data and field data further amplifies this confusion: a site can be green in Lighthouse and orange in the CrUX Report.

What Are the Concrete Cases Where CWV Fail to Measure Performance?

Consider sites with dynamic or personalized content. A page that loads content tailored to the user profile may show an acceptable CLS for 80% of visitors but catastrophic for the remaining 20% depending on their network configuration. The CWV average out this data — but Google does not weigh it according to the actual quality of the experience.

Another example: sites with optimized progressive loading. A site may display critical content (above-the-fold) instantly and then load the rest via lazy loading. The user perceives immediate speed, but the technical LCP may be degraded if the "largest" element, in the strict sense, loads late. Metrics measure what is measurable — not always what matters.

Single Page Applications (SPA) architectures also pose a problem. A transition between pages via JavaScript may be perceived as instantaneous by the user, but CWV do not capture these micro-interactions — they remain focused on the initial loading of the page. A structural disconnect between the metric and actual usage.

Is This Ongoing Evolution of Metrics Really Good News?

Google states that CWV are continuing to evolve. In theory, this is positive: metrics that refine to better match reality. In practice, it means that the rules of the game are changing regularly. The introduction of INP (Interaction to Next Paint) to replace FID is a perfect illustration — some sites have had to completely rethink their optimization strategy.

This methodological instability poses a problem for ROI and prioritization. Investing heavily in optimizing CLS today is betting on a metric that could be revised tomorrow. Technical teams must juggle compliance with current standards and anticipation of future evolutions. A constant balancing act.

• CWV measure approximations, not user reality in all its complexity
• Fast sites can be poorly rated due to methodological biases (SPA, lazy loading, dynamic content)
• The continuous evolution of metrics creates instability in long-term optimization strategies
• The lab/field gap amplifies confusion between what tools measure and what users experience
• False positives and false negatives are acknowledged by Google itself, questioning the reliability of the ranking signal

Is This Statement Consistent with Field Observations?

Yes — and it is even one of the few Google statements that validates what SEOs have been observing for months. In the field, we regularly see sites with excellent CWV scores stagnating in positions 8-12, while competitors showing orange or even red dominate the top 3. The correlation between CWV and ranking remains weak, especially for competitive queries where content relevance outweighs performance signal.

But be careful — this does not mean that CWV have no impact. For queries where several pages are nearly equivalent in terms of content and authority, user experience can make the difference. The problem is that Google never communicates the actual weight of this factor. [To be verified]: is it a marginal tie-breaker or a significant ranking signal? Public data does not allow a decisive answer.

What Nuances Should Be Applied to This Acknowledgment of Imperfection?

Google states that metrics are evolving — but this evolution is slow, opaque, and often lagging behind the technical innovations of the web. INP took years to emerge, while FID was clearly insufficient. In the meantime, how many sites have over-optimized for a shaky indicator? How many technical budgets misallocated?

Second nuance: acknowledging imperfection does not change the rules of the game. Google continues to use CWV as a ranking signal, despite their biases. A "truly fast" site according to Martin Splitt but with poor CWV scores remains penalized — or at least, not rewarded. The admission of imperfection is almost cosmetic if the algorithmic consequences remain unchanged.

Finally, this statement suggests that Google is working on more refined metrics. But which ones? When? With what impact on already optimized sites? Ambiguity persists. [To be verified]: is there a public roadmap for CWV evolutions or are we still in a perpetual wait for drip-fed announcements?

Should We Therefore Abandon Optimizing Core Web Vitals?

No — but we need to reposition this optimization within a global strategy. CWV are neither a religion nor a panacea. They are indicators among others, useful but imperfect. Completely abandoning performance optimization would be a mistake: even if the metrics are shaky, a smooth user experience remains beneficial for conversion rates, bounce rates, and engagement.

The real question lies in the trade-off between CWV optimization and other SEO levers. If your site has weak content, nonexistent backlinks, and a strictly siloed architecture, spending three months scraping 200 milliseconds off LCP will change nothing about your ranking. Prioritize. CWV should be part of continuous improvement, not at the top of the roadmap if other fundamentals are faulty.

How to Measure Actual Performance Beyond CWV?

Let's be clear: CWV should not be your only source of truth. Cross-reference them with real business metrics: average time on page, bounce rate, conversion rate, scroll depth. If your CWV are orange but user engagement and conversions are top-notch, your real experience may be better than what Google measures.

Use the CrUX Report in BigQuery to analyze your field data at the 75th percentile — this is the threshold Google uses to determine if a page turns green. But go further: look at the complete distribution. If 60% of your users have an excellent experience but 25% are suffering (slow network, old devices), you have a real problem even if the CWV pass. Averages hide extremes.

What Mistakes to Avoid in Core Web Vitals Optimization?

Error #1: Optimizing for Lighthouse Instead of the CrUX Report. Lighthouse measures a simulated experience in a lab, on a controlled network and a standardized device. The CrUX measures your actual users, on their real devices, under their actual network conditions. It’s the CrUX that matters for Google — not your Lighthouse score of 98/100.

Error #2: Degrading UX to Improve Metrics. Removing useful JavaScript features to reduce TBT. Loading an ugly placeholder to improve visual LCP. Blocking scroll to avoid CLS. These "optimizations" degrade the real experience — exactly what Splitt points out. A good CWV score that kills conversion is a failure, not a victory.

Error #3: Ignoring Data Segmentation. Your CWV vary according to the device (mobile vs desktop), type of connection (4G vs WiFi vs fiber), and geography. A site can be green on desktop and red on mobile. Analyze by segment — and prioritize the one that represents the majority of your organic traffic.

What Concrete Actions Should Be Taken to Navigate This Acknowledged Imperfection?

Adopt a hybrid approach: optimize CWV without sanctifying them. Aim for green on the three main metrics (LCP, CLS, INP) without sacrificing critical features or real user experience. If a technical trade-off forces you to choose between a good CWV score and a better UX, choose UX — even if it means accepting an orange on the metrics.

Document and monitor. Create baselines before/after each optimization and measure the impact not only on CWV but also on organic traffic, CTR, time spent, conversions. If a CWV optimization improves your scores but degrades your business, rollback. Metrics are means, not ends.

Finally, stay alert for developments. Google states that CWV continue to improve — watch for official announcements (Chrome Dev Blog, web.dev, Google Search Central). Anticipate changes rather than endure them. INP has replaced FID — the next metric will come sooner or later. Prepare your technical infrastructure to absorb these changes without a complete overhaul.

• Analyze your real CrUX data (Search Console + BigQuery) rather than relying solely on Lighthouse
• Cross-reference CWV with business metrics (conversion, engagement, time on page) to detect discrepancies
• Segment your data by device, connection, geo to identify where the real problems lie
• Prioritize real UX over metric optimization: an orange with good UX is worth more than a degraded green
• Document baselines before/after and measure the business impact of each CWV optimization
• Monitor Google announcements on metric evolutions to anticipate upcoming changes