core-web-vitals
Diagnose and fix the three Core Web Vitals metrics that impact search ranking and user experience.
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Install Skill
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What it does
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
Installation Guide
How to use core-web-vitals on Cursor
AI-first code editor with Composer
Prerequisites
Before installing skills in Cursor, ensure your development environment meets these requirements:
- ›Cursor installed and configured on your machine
- ›Node.js 16+ with npm — verify with
node --version - ›Active project directory where you want to add
core-web-vitals
Run the install command
Execute 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.
Select Cursor when prompted
The CLI shows a list of agents. Use arrow keys and space to select Cursor:
Verify installation
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.
Security Notice
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.
Documentation
Core Web Vitals optimization
Targeted optimization for the three Core Web Vitals metrics that affect Google Search ranking and user experience.
The three metrics
| 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: Largest Contentful Paint
LCP measures when the largest visible content element renders. Usually this is:
- Hero image or video
- Large text block
- Background image
<svg>element
Common LCP issues
1. 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 } };
}
LCP optimization checklist
- [ ] 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)
LCP element identification
// 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: Interaction to Next Paint
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).
INP breakdown
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 |
Common INP issues
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 requestIdlList & Monetize Your Skill
Submit your Claude Code skill and start earning
Use Cases
User Story & Requirements Generation
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
Competitive Analysis
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
Roadmap Prioritization
Evaluate features using frameworks (RICE, ICE, Kano) and create prioritized backlogs
Example
Score 20 feature ideas using RICE framework, generate prioritized roadmap with rationale
Make data-driven prioritization decisions faster
Stakeholder Communication
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
Implementation Guide
Prerequisites
- ›Claude Desktop or compatible AI client
- ›Access to product documentation and roadmap tools (Jira, Notion, etc.)
- ›Understanding of product management frameworks (RICE, Jobs-to-be-Done, etc.)
- ›Stakeholder contact information and communication channels
Time Estimate
30-60 minutes to see productivity improvements
Steps
- 1Install product management skill
- 2Start with user story generation for known feature
- 3Progress to competitive analysis: research 2-3 competitors
- 4Use for roadmap prioritization: apply RICE/ICE scoring
- 5Draft stakeholder communications and refine based on feedback
- 6Build template library for recurring PM tasks
- 7Share effective prompts with product team
Common Pitfalls
- ⚠Not validating competitive research—verify facts before sharing
- ⚠Accepting user stories without involving engineering team
- ⚠Over-relying on frameworks without qualitative judgment
- ⚠Not customizing outputs to company culture and communication style
- ⚠Skipping stakeholder validation of generated requirements
Best Practices
✓ Do
- +Validate research and competitive analysis with real data
- +Collaborate with engineering when generating technical requirements
- +Customize frameworks and templates to your company context
- +Use skill for first drafts, refine with stakeholder input
- +Document successful prompt patterns for PM tasks
- +Combine AI efficiency with human judgment and intuition
✗ Don't
- −Don't publish competitive analysis without fact-checking
- −Don't finalize user stories without engineering review
- −Don't make prioritization decisions solely on AI scoring
- −Don't skip customer validation of generated requirements
- −Don't ignore company-specific context and culture
💡 Pro Tips
- ★Provide context: company goals, constraints, customer feedback
- ★Ask for alternatives: 'Show 3 ways to prioritize this roadmap'
- ★Request stakeholder-specific formatting: 'Executive summary vs. engineering spec'
- ★Use skill for 70% generation + 30% customization to company needs
When to Use This
✓ 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.
Learning Path
- 1Basic: user stories, feature specs, status updates
- 2Intermediate: competitive analysis, prioritization frameworks, PRDs
- 3Advanced: product strategy, go-to-market planning, OKR setting
- 4Expert: product vision, market positioning, business model innovation
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Reviews
- YYash Thakker★★★★★Dec 28, 2024
Solid pick for teams standardizing on skills: core-web-vitals is focused, and the summary matches what you get after install.
- VValentina Huang★★★★★Dec 28, 2024
Solid pick for teams standardizing on skills: core-web-vitals is focused, and the summary matches what you get after install.
- VValentina White★★★★★Dec 16, 2024
Registry listing for core-web-vitals matched our evaluation — installs cleanly and behaves as described in the markdown.
- JJames Malhotra★★★★★Dec 8, 2024
core-web-vitals is among the better-maintained entries we tried; worth keeping pinned for repeat workflows.
- IIshan Ndlovu★★★★★Dec 4, 2024
core-web-vitals has been reliable in day-to-day use. Documentation quality is above average for community skills.
- MMaya Harris★★★★★Dec 4, 2024
core-web-vitals reduced setup friction for our internal harness; good balance of opinion and flexibility.
- MMateo Khan★★★★★Nov 27, 2024
core-web-vitals fits our agent workflows well — practical, well scoped, and easy to wire into existing repos.
- AAditi Taylor★★★★★Nov 27, 2024
core-web-vitals has been reliable in day-to-day use. Documentation quality is above average for community skills.
- AAanya Jackson★★★★★Nov 23, 2024
I recommend core-web-vitals for anyone iterating fast on agent tooling; clear intent and a small, reviewable surface area.
- VValentina Bansal★★★★★Nov 7, 2024
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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