Diagnose and fix the three Core Web Vitals metrics that impact search ranking and user experience.
Works with
Covers LCP (Largest Contentful Paint), INP (Interaction to Next Paint), and CLS (Cumulative Layout Shift) with specific thresholds and optimization strategies for each
Includes common causes, code examples, and debugging scripts for identifying bottlenecks in loading, interactivity, and visual stability
Provides framework-specific quick fixes for Next.js, React, and Vue/Nuxt, plus measu
AI-first code editor with Composer
Before installing skills in Cursor, ensure your development environment meets these requirements:
node --versioncore-web-vitalsExecute the skills CLI command in your project's root directory to begin installation:
Fetches core-web-vitals from addyosmani/web-quality-skills and configures it for Cursor.
The CLI shows a list of agents. Use arrow keys and space to select Cursor:
Confirm successful installation by checking the skill directory location:
Restart Cursor to activate core-web-vitals. Access via /core-web-vitals in your agent's command palette.
We perform automated surface-level scans (Gen AI Scanner, Socket, Snyk) during installation. These checks detect common vulnerabilities but do not guarantee complete security. Always review skill source code and verify the publisher's reputation before production use.
Skills execute code in your environment. Always review source, verify the publisher, and test in isolation before production.
Submit your Claude Code skill and start earning
Create detailed user stories, acceptance criteria, and feature specs
Example
Generate user stories for 'password reset feature' with acceptance criteria, edge cases, and test scenarios
Reduce spec writing time by 50%, ensure comprehensive coverage
Research competitors, compare features, identify gaps
Example
Analyze 5 competitor products, create feature comparison matrix, suggest differentiation opportunities
Complete competitive research in 2 hours instead of 2 days
Evaluate features using frameworks (RICE, ICE, Kano) and create prioritized backlogs
Example
Score 20 feature ideas using RICE framework, generate prioritized roadmap with rationale
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Targeted optimization for the three Core Web Vitals metrics that affect Google Search ranking and user experience.
| Metric | Measures | Good | Needs work | Poor |
|---|---|---|---|---|
| LCP | Loading | ≤ 2.5s | 2.5s – 4s | > 4s |
| INP | Interactivity | ≤ 200ms | 200ms – 500ms | > 500ms |
| CLS | Visual Stability | ≤ 0.1 | 0.1 – 0.25 | > 0.25 |
Google measures at the 75th percentile — 75% of page visits must meet "Good" thresholds.
LCP measures when the largest visible content element renders. Usually this is:
<svg> element1. Slow server response (TTFB > 800ms)
Fix: CDN, caching, optimized backend, edge rendering
2. Render-blocking resources
<!-- ❌ Blocks rendering -->
<link rel="stylesheet" href="/all-styles.css">
<!-- ✅ Critical CSS inlined, rest deferred -->
<style>/* Critical above-fold CSS */</style>
<link rel="preload" href="/styles.css" as="style"
onload="this.onload=null;this.rel='stylesheet'">
3. Slow resource load times
<!-- ❌ No hints, discovered late -->
<img src="/hero.jpg" alt="Hero">
<!-- ✅ Preloaded with high priority -->
<link rel="preload" href="/hero.webp" as="image" fetchpriority="high">
<img src="/hero.webp" alt="Hero" fetchpriority="high">
4. Client-side rendering delays
// ❌ Content loads after JavaScript
useEffect(() => {
fetch('/api/hero-text').then(r => r.json()).then(setHeroText);
}, []);
// ✅ Server-side or static rendering
// Use SSR, SSG, or streaming to send HTML with content
export async function getServerSideProps() {
const heroText = await fetchHeroText();
return { props: { heroText } };
}
- [ ] TTFB < 800ms (use CDN, edge caching)
- [ ] LCP image preloaded with fetchpriority="high"
- [ ] LCP image optimized (WebP/AVIF, correct size)
- [ ] Critical CSS inlined (< 14KB)
- [ ] No render-blocking JavaScript in <head>
- [ ] Fonts don't block text rendering (font-display: swap)
- [ ] LCP element in initial HTML (not JS-rendered)
// Find your LCP element
new PerformanceObserver((list) => {
const entries = list.getEntries();
const lastEntry = entries[entries.length - 1];
console.log('LCP element:', lastEntry.element);
console.log('LCP time:', lastEntry.startTime);
}).observe({ type: 'largest-contentful-paint', buffered: true });
INP measures responsiveness across ALL interactions (clicks, taps, key presses) during a page visit. It reports the worst interaction (at 98th percentile for high-traffic pages).
Total INP = Input Delay + Processing Time + Presentation Delay
| Phase | Target | Optimization |
|---|---|---|
| Input Delay | < 50ms | Reduce main thread blocking |
| Processing | < 100ms | Optimize event handlers |
| Presentation | < 50ms | Minimize rendering work |
1. Long tasks blocking main thread
// ❌ Long synchronous task
function processLargeArray(items) {
items.forEach(item => expensiveOperation(item));
}
// ✅ Break into chunks with yielding
async function processLargeArray(items) {
const CHUNK_SIZE = 100;
for (let i = 0; i < items.length; i += CHUNK_SIZE) {
const chunk = items.slice(i, i + CHUNK_SIZE);
chunk.forEach(item => expensiveOperation(item));
// Yield to main thread
await new Promise(r => setTimeout(r, 0));
// Or use scheduler.yield() when available
}
}
2. Heavy event handlers
// ❌ All work in handler
button.addEventListener('click', () => {
// Heavy computation
const result = calculateComplexThing();
// DOM updates
updateUI(result);
// Analytics
trackEvent('click');
});
// ✅ Prioritize visual feedback
button.addEventListener('click', () => {
// Immediate visual feedback
button.classList.add('loading');
// Defer non-critical work
requestAnimationFrame(() => {
const result = calculateComplexThing();
updateUI(result);
});
// Use requestIdlMake data-driven prioritization decisions faster
Draft PRDs, status updates, and stakeholder presentations
Example
Create executive summary of Q3 roadmap, monthly progress report, feature launch announcement
Save 3-5 hours/week on communication overhead
Prerequisites
Time Estimate
30-60 minutes to see productivity improvements
Steps
Common Pitfalls
✓ Do
✗ Don't
💡 Pro Tips
✓ Use when
Use for user story writing, competitive research, roadmap prioritization, stakeholder communication, and PRD drafting. Best for reducing repetitive documentation and research work.
✗ Avoid when
Avoid for strategic product vision (requires deep customer empathy), pricing decisions (needs market and financial expertise), or when face-to-face customer discovery is more valuable than speed.
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Solid pick for teams standardizing on skills: core-web-vitals is focused, and the summary matches what you get after install.
Solid pick for teams standardizing on skills: core-web-vitals is focused, and the summary matches what you get after install.
Registry listing for core-web-vitals matched our evaluation — installs cleanly and behaves as described in the markdown.
core-web-vitals is among the better-maintained entries we tried; worth keeping pinned for repeat workflows.
core-web-vitals has been reliable in day-to-day use. Documentation quality is above average for community skills.
core-web-vitals reduced setup friction for our internal harness; good balance of opinion and flexibility.
core-web-vitals fits our agent workflows well — practical, well scoped, and easy to wire into existing repos.
core-web-vitals has been reliable in day-to-day use. Documentation quality is above average for community skills.
I recommend core-web-vitals for anyone iterating fast on agent tooling; clear intent and a small, reviewable surface area.
Useful defaults in core-web-vitals — fewer surprises than typical one-off scripts, and it plays nicely with `npx skills` flows.
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