Core Web Vitals

Brass-SEO treats this as the authoritative threshold reference for all CWV reporting. Google defines three active Core Web Vitals: Largest Contentful Paint must be at or under 2.5 seconds for Good; Interaction to Next Paint must be at or under 200 milliseconds for Good; and Cumulative Layout Shift must be at or under 0.1 for Good. Pages exceeding the 4.0 second LCP, 500 millisecond INP, or 0.25 CLS thresholds are classified as Poor. These thresholds are derived from Chrome real-user data at the 75th percentile of page loads.

Examines:

Google's official Core Web Vitals specification — threshold values for LCP, INP, and CLS, with the 75th-percentile measurement methodology.

Brass-SEO draws on:

The LCP ≤2.5s, INP ≤200ms, CLS ≤0.1 threshold values — the exact benchmarks Brass-SEO's page audit reports against.

Primary source

web.dev/articles/vitals

Brass-SEO monitors this for industry benchmarks. The 2024 Web Almanac Performance chapter reports that 43% of mobile sites achieve good Core Web Vitals across all three metrics, down from 48% after Google replaced FID with INP in March 2024. The 5-percentage-point drop reveals hidden interactivity debt — sites that passed under FID failed under INP's stricter measurement of total interaction latency from pointer to next paint. Nearly 6 in 10 mobile sites still fail at least one CWV threshold. Brass-SEO uses this data to contextualize a site's CWV status relative to the broader web.

Examines:

Annual independent measurement of Core Web Vitals pass rates, trend analysis, and technology adoption across millions of origins from real Chrome user data.

Brass-SEO draws on:

The 43% mobile pass rate and FID-to-INP transition data — used to contextualize a site's CWV status in Brass-SEO's page audit output.

Primary source

almanac.httparchive.org/en/2024/performance

Brass-SEO draws on this to explain how Google measures real-user performance. The Chrome User Experience Report collects field data from opted-in Chrome users and is the dataset Google uses to determine whether a URL achieves Good, Needs Improvement, or Poor on each Core Web Vitals metric for ranking purposes. Lab tests — Lighthouse, PageSpeed Insights lab mode — simulate conditions but do not determine ranking eligibility. A page can score 100 in Lighthouse and still receive a Poor CWV signal in Google's ranking assessment if real users on slower connections experience poor performance.

Examines:

Google's Chrome User Experience Report — the dataset of real Chrome user performance measurements that powers CWV ranking assessments.

Brass-SEO draws on:

The distinction between lab data and field data — cited when explaining why PageSpeed Insights lab scores may differ from GSC's Core Web Vitals report.

Primary source

developer.chrome.com/docs/crux

Brass-SEO cites this when scoping CWV's importance relative to content quality. Google's documentation confirms Core Web Vitals became a ranking signal in May 2021 for mobile and February 2022 for desktop. Google explicitly states in this document that great page experience does not override having great content — a page with strong content will rank even with poor experience signals. CWV is a tiebreaker among pages of comparable quality, not a dominant standalone ranking factor. Brass-SEO uses this framing to scope CWV recommendations correctly.

Examines:

Google's official documentation of the Page Experience ranking update — which signals it includes, when it launched for mobile and desktop, and its stated weight relative to content quality.

Brass-SEO draws on:

The tiebreaker framing of CWV — used to correctly scope CWV importance in Brass-SEO's page audit recommendations rather than overstating its ranking impact.

Primary source

developers.google.com/search/docs/appearance/page-experience

Brass-SEO uses this to explain the diagnostic tool stack. PageSpeed Insights combines real-user CrUX field data with Lighthouse lab diagnostics in a single report. The field data section shows actual CWV status from Chrome users and is what affects ranking eligibility; the lab section provides Lighthouse scores on a 0–100 scale from a simulated throttled mid-tier mobile device. Lighthouse scores and field data can diverge significantly. The tool provides specific opportunity items — render-blocking resources, unused JavaScript, image format recommendations — with estimated savings in milliseconds.

Examines:

Google's PageSpeed Insights tool documentation and Lighthouse methodology — the distinction between field data (CrUX) and lab scores, and how to read each section.

Brass-SEO draws on:

The field vs. lab data distinction — cited in Brass-SEO's page audit to explain why PSI lab score and GSC CWV status can diverge.

Primary source

developers.google.com/speed/docs/insights/v5/about