Skip to main content

​
Core Web Vitals Thresholds

Core Web Vitals are the three metrics that Google uses for search ranking and page experience evaluation. Values are measured at the 75th percentile of page visits.
To rank well in Google Search, 75% of your page visits must meet the “Good” threshold for all three metrics.

​
The Three Metrics

Largest Contentful Paint (LCP)Measures when the largest visible content element renders. Usually:
  • Hero image or video
  • Large text block
  • Background image (with CSS)
  • SVG element
Target: ≤ 2.5 secondsCommon issues:
  • Slow server response (TTFB > 800ms)
  • Render-blocking resources
  • Slow resource load times
  • Client-side rendering delays

​
Lighthouse Score Targets

Lighthouse audits produce scores from 0-100 for each category. These are the recommended target scores:
Unlike other categories where some issues are recommendations, accessibility issues directly impact users’ ability to access your content. A score below 100 means some users cannot fully use your site. This is both an ethical concern and a legal risk in many jurisdictions.

​
Performance Score Breakdown

Lighthouse Performance score is weighted:
INP (Interaction to Next Paint) is measured separately as a Core Web Vital and is not part of the Lighthouse Performance score calculation, though it’s reported in Lighthouse 10+.

​
Performance Budget Recommendations

Performance budgets help prevent regression. These budgets assume 3G network connection (4 Mbps):

​
Resource Size Budgets

Why 300 KB compressed?
  • 300 KB gzipped ≈ 900 KB uncompressed
  • Parse time: ~100-200ms on mid-tier mobile
  • Execution time: Varies by code complexity
  • Total impact: Can block main thread for 300-500ms
Budget strategy:
  • Critical JS: < 50 KB (inline or preloaded)
  • Main bundle: < 150 KB
  • Lazy-loaded routes: < 100 KB each

​
Timing Budgets

​
Accessibility Conformance Levels

WCAG 2.1 defines three conformance levels. Most organizations target Level AA as it balances accessibility with implementation practicality:

​
WCAG 2.1 Level AA Requirements

Text Alternatives (1.1)
  • All images must have alt text
  • Decorative images: alt=""
  • Complex images: Use aria-describedby
Color Contrast (1.4.3)Media Alternatives (1.2)
  • Videos must have captions
  • Audio must have transcripts
  • Pre-recorded video should have audio descriptions (AA)
Keyboard Accessible (2.1)
  • All functionality available via keyboard
  • No keyboard traps
  • Skip links provided
Focus Visible (2.4.7)
  • Focus indicators must have 3:1 contrast ratio
  • Focus indicators always visible (never outline: none without replacement)
Timing (2.2)
  • Users can extend time limits
  • No auto-advancing content without pause control
Target Size (2.5.5 - Level AAA, recommended)
  • Interactive elements: ≥ 44×44 CSS pixels
  • Mobile tap targets: ≥ 48×48 CSS pixels (recommended)
Page Language (3.1.1)
  • <html lang="en"> must be set
  • Language changes marked: <span lang="fr">
Consistent Navigation (3.2.3)
  • Navigation order consistent across pages
  • Navigation mechanisms in same location
Error Identification (3.3.1)
  • Form errors clearly described
  • Error messages associated with fields (aria-describedby)
Labels (3.3.2)
  • All form inputs have labels
  • Labels visible (not placeholder-only)
Valid HTML (4.1.1)
  • No duplicate IDs
  • Properly nested elements
  • Valid ARIA attributes
Name, Role, Value (4.1.2)
  • Interactive elements have accessible names
  • Correct ARIA roles
  • State changes announced

​
SEO Thresholds

While SEO doesn’t have strict “pass/fail” thresholds like Core Web Vitals, these are recommended targets:

​
On-Page SEO Targets

​
Technical SEO Targets

​
Page Speed Targets for SEO

Google considers page speed as a ranking factor, especially for mobile:
Mobile performance is more important for SEO since Google uses mobile-first indexing.

​
Security Best Practices Thresholds

​
Security Headers Scores

​
Vulnerability Thresholds

​
Summary Table: All Critical Thresholds

Quick reference for the most important thresholds: