Best Free Online Developer Tools to Use in 2026
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Aug 08, 2026
Core Web Vitals Calculator
Calculate and analyze your Core Web Vitals scores with pass/fail grading and optimization recommendations.
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Enter Your Metrics
Enter your Core Web Vitals values from Lighthouse, PageSpeed Insights, or your RUM provider.
Largest Contentful Paint
First Input Delay
Cumulative Layout Shift
Interaction to Next Paint
Time to First Byte (good ≤ 800ms)
Vitals Scorecard
Prioritized Recommendations
What are Core Web Vitals?
Core Web Vitals are a set of real-world metrics that measure key aspects of user experience on the web. They are part of Google's Page Experience signals and impact search rankings. The three core metrics are LCP (loading), FID/INP (interactivity), and CLS (visual stability).
This calculator helps you evaluate your metrics against Google's recommended thresholds, identify which vitals need improvement, and provides actionable recommendations for optimization.
How to Use
- Get Your Metrics — Run Lighthouse in Chrome DevTools, use PageSpeed Insights, or check your RUM (Real User Monitoring) provider.
- Enter Values — Input your LCP (in seconds), FID (in ms), CLS, INP (in ms), and TTFB (in ms) into the fields above.
- Review Scorecard — Each vital is graded as Good (green), Needs Improvement (orange), or Poor (red) based on Google thresholds.
- Check Recommendations — View prioritized optimization suggestions for any vitals that need improvement.
Frequently Asked Questions
What are the Google threshold values?
LCP: Good ≤ 2.5s, Poor > 4.0s. FID: Good ≤ 100ms, Poor > 300ms. CLS: Good ≤ 0.1, Poor > 0.25. INP: Good ≤ 200ms, Poor > 500ms. TTFB: Good ≤ 800ms, Poor > 1800ms. These thresholds are defined by Google and used in Page Experience ranking signals.
How do I measure Core Web Vitals?
You can measure Core Web Vitals using Google PageSpeed Insights, Chrome DevTools Lighthouse panel, the Web Vitals Chrome extension, or Real User Monitoring (RUM) tools like Google Analytics, Cloudflare Browser Insights, or Sentry.
What is the difference between FID and INP?
FID (First Input Delay) measures the time from the first user interaction to when the browser can process the event. INP (Interaction to Next Paint) is a newer metric that measures the latency of all interactions, not just the first one. INP will replace FID as a Core Web Vital in March 2024.
Is my data stored?
No. Everything runs entirely in your browser. Your data is never sent to any server.
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