Core Web Vitals Analyzer
A Core Web Vitals analyzer audits Google's three official user experience metrics: Largest Contentful Paint (LCP ≤ 2.5s), Interaction to Next Paint (INP ≤ 200ms), and Cumulative Layout Shift (CLS ≤ 0.10). It evaluates rolling 28-day 75th percentile Chrome User Experience Report (CrUX) field data alongside synthetic lab benchmarks.
Click to choose or drop a Lighthouse JSON report here
Extracts LCP, INP, CLS, FCP, and TBT metrics locally with zero data transfer.
Supporting Diagnostic Lab Vitals
What is a Core Web Vitals analyzer and when should you use it?
The Core Web Vitals Analyzer is a technical performance assessment tool dedicated to auditing the three standardized user-experience pillars established by the Google Chrome team: Largest Contentful Paint (loading performance), Interaction to Next Paint (page responsiveness), and Cumulative Layout Shift (visual stability). Under Google's search ranking algorithms, meeting the 75th percentile threshold across all three Core Web Vitals is an essential prerequisite for optimizing page experience signals. This tool enables developers and webmasters to analyze live URLs via Google's PageSpeed Insights API or evaluate pre-computed Lighthouse JSON reports completely offline. It provides a transparent, side-by-side comparison of synthetic Lab metrics against authentic 28-day rolling Field data sourced from the Chrome User Experience Report (CrUX). Crucially, the analyzer respects the operational distinction between lab and field conditions: while Total Blocking Time (TBT) serves as an informative lab proxy for main-thread contention, it is never falsely equated with real-user INP. When field data is unavailable due to insufficient traffic, the analyzer flags the condition cleanly rather than fabricating estimates. To diagnose specific bottlenecks revealed in your vitals report, run the Google PageSpeed Score Checker for a top-level category review, evaluate device differences with the Mobile vs Desktop Speed Comparator, optimize hero assets with the Largest Contentful Paint Analyzer, eliminate layout jumps using the Cumulative Layout Shift Analyzer, and unblock browser rendering using the Render Blocking Resources Finder. Further accelerate asset delivery by using the Unused CSS Opportunity Finder, optimizing media payloads with the Image Performance Opportunity Finder, auditing main-thread execution using the JavaScript Performance Audit, and reviewing accessibility with the Website Accessibility Audit Summary. Explore our complete Website Performance & Core Web Vitals Tools and Technical SEO Audit Tools categories, or verify your server response times using the HTTP Status Code Checker.
How do you use it?
- Input your target URL or upload an exported Lighthouse / CrUX JSON report.
- Choose between Mobile or Desktop emulation to review form-factor specific performance.
- Click "Audit Core Web Vitals" to execute the analysis or "Load Sample Report" for an immediate demonstration.
- Examine the three core metrics (LCP, INP, and CLS) evaluated against Google's official Good, Needs Improvement, and Poor thresholds.
- Review supporting diagnostic vitals including First Contentful Paint (FCP) and Total Blocking Time (TBT).
- Analyze the actionable technical guidance for elements causing layout shifts, delayed hero renders, or script-blocked interactions.
Working on a comprehensive technical audit? Browse all free SEO tools to discover the next step in your workflow, or contact our technical support team if you require a specialized custom utility.
Result interpretation & practical applications
When evaluating the output of the Core Web Vitals analyzer, review the parsed metrics against your specific site architecture. Outputs are formatted for direct implementation into your HTML source, web server configuration, or Google Search Console audit files.
Always inspect generated values for contextual nuance. Automated tools highlight structural patterns, but manual verification confirms that technical directives align with your overarching SEO strategy.
Technical rules and limitations
- Official 75th Percentile Standard: Core Web Vitals compliance is assessed at the 75th percentile of all page visits recorded over 28 rolling days.
- LCP Metric Thresholds: Good (≤ 2.5 seconds), Needs Improvement (2.5 s to 4.0 seconds), Poor (> 4.0 seconds).
- INP Metric Thresholds: Good (≤ 200 milliseconds), Needs Improvement (200 ms to 500 milliseconds), Poor (> 500 milliseconds).
- CLS Metric Thresholds: Good (≤ 0.10 score), Needs Improvement (0.10 to 0.25 score), Poor (> 0.25 score).
- Metric Isolation: INP is exclusively derived from real-user CrUX field data and is never synthesized from lab Total Blocking Time (TBT).
Common mistakes and troubleshooting
- Confusing synthetic lab tests with field data and assuming a fast lab test guarantees a passing grade in Google Search Console.
- Treating Total Blocking Time (TBT) as a direct replacement for Interaction to Next Paint (INP) without measuring actual user interactions.
- Neglecting Cumulative Layout Shift caused by dynamically injected web fonts or third-party advertising containers lacking aspect ratios.
- Auditing only desktop network connections while the vast majority of Google crawlers evaluate sites via mobile user-agent emulation.
No tool can promise how a search engine will crawl, index, or rank your pages. This tool generates and validates code against documented technical specifications; you determine where to deploy it, and you should always test changes on staging environments first. Google publishes extensive guidelines in Search Central on evaluating third-party SEO tools and advice. Learn more about our technical testing standards on our about us page, or explore full site audits on our pricing page.
Related free tools & workflows
Browse all Website Performance & Core Web Vitals Tools →Technical SEO Audit Workflows
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Authoritative Technical Documentation & Standards
This tool executes logic aligned with official technical documentation and search engine webmaster standards:
- Google Search Central page experience guide
Google Search Central: Core Web Vitals and Page Experience in Google Search
Primary engineering source and technical documentation.
- web.dev Core Web Vitals learning guide
web.dev: Learn Core Web Vitals Metrics and Thresholds
Primary engineering source and technical documentation.
Core Web Vitals Analyzer questions
What happens if my site fails one Core Web Vital but passes the other two? ↓
To achieve an overall passing Core Web Vitals status in Google Search Console and Chrome UX reports, a page must achieve a "Good" rating across all three core metrics (LCP, INP, and CLS) at the 75th percentile. Failing even one metric results in a failing overall assessment.
Why is Interaction to Next Paint (INP) not measured in synthetic lab tests? ↓
INP measures the latency of real user interactions (such as clicks, taps, and keyboard inputs) throughout the entire lifespan of a webpage. Because synthetic automated lab crawlers do not click around pages like genuine humans, INP can only be authentically recorded from real-user field telemetry.
How does Cumulative Layout Shift (CLS) impact search rankings and conversions? ↓
CLS measures visual instability. Unexpected layout shifts disorient users, cause accidental clicks on incorrect links or ads, and directly signal poor user experience to Google's ranking algorithms.
Is this tool free? ↓
Yes. It is completely free to use and requires no registration or subscription.
Does this tool visit my website or store my files? ↓
No. It executes entirely in your local browser runtime. Your inputs and results are never stored or logged on our servers.
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