Frontend Engineering Tools
Core Web Vitals Reference
Search Core Web Vitals metrics by name or optimization scenario. Covers LCP, INP (replacing FID), CLS, FCP, and TTFB thresholds with SEO impact.
No data is transmitted — everything runs locallyTool
About this tool
Core Web Vitals Reference
The Core Web Vitals Reference covers LCP, INP, CLS, FCP, and TTFB thresholds with Good/Needs Improvement/Poor tiers, SEO ranking impact, and optimization guidance.
• Look up CLS threshold before investigating a layout shift issue
• Reference INP thresholds after the March 2024 metric change from FID
• Find LCP optimization techniques before a performance audit
• Understand Core Web Vitals Google ranking impact before prioritizing work
Next step
Accessibility Color Contrast Checker — Calculate WCAG 2.1 color contrast ratio and check AA/AAA compliance.
Open Accessibility Color Contrast Checker →
FAQ
What does this tool tell you?
The Core Web Vitals Reference covers LCP, INP, CLS, FCP, and TTFB thresholds with Good/Needs Improvement/Poor tiers, SEO ranking impact, and optimization guidance.
What affects the result most?
LCP (Largest Contentful Paint): Good <2.5s, Needs Improvement 2.5-4s, Poor >4s — largest image or text block. FID → INP (Interaction to Next Paint, March 2024): Good <200ms, Needs Improvement 200-500ms, Poor >500ms. CLS (Cumulative Layout Shift): Good <0.1, Needs Improvement 0.1-0.25, Poor >0.25 — caused by images without dimensions.
How should I use the result?
Use this tool to orient quickly to the concepts, field names, or values you are about to look up in a full specification or vendor documentation. It summarizes the common cases; the authoritative source remains whichever standard or vendor doc defines the values themselves.
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