--- name: "core-web-vitals" description: "Core Web Vitals optimization workflow skill. Use this skill when the user needs Optimize Core Web Vitals (LCP, INP, CLS) for better page experience and search ranking. Use when asked to \"improve Core Web Vitals\", \"fix LCP\", \"reduce CLS\", \"optimize INP\", \"page experience optimization\", or \"fix layout shifts\". Focuses specifically on the three Core Web Vitals metrics. Do NOT use for general web performance (use perf-web-optimization), Lighthouse audits (use perf-lighthouse), or Astro-specific optimization (use perf-astro) and the operator should preserve the upstream workflow, copied support files, and provenance before merging or handing off." version: "0.0.1" category: "frontend" tags: - "core-web-vitals" - "optimize" - "core" - "web" - "vitals" - "lcp" - "inp" - "cls" - "omni-enhanced" complexity: "advanced" risk: "safe" tools: - "codex-cli" - "claude-code" - "cursor" - "gemini-cli" - "opencode" source: "omni-team" author: "Omni Skills Team" date_added: "2026-04-14" date_updated: "2026-04-26" source_type: "omni-curated" maintainer: "Omni Skills Team" family_id: "core-web-vitals" family_name: "Core Web Vitals optimization" variant_id: "omni" variant_label: "Omni Curated" is_default_variant: true derived_from: "skills/core-web-vitals" upstream_skill: "skills/core-web-vitals" upstream_author: "web-quality-skills" upstream_source: "community" upstream_pr: "133" upstream_head_repo: "diegosouzapw/awesome-omni-skills" upstream_head_sha: "9f1c34bd96b4fc03578ceb26f6303d8bf2c13b42" curation_surface: "skills_omni" enhanced_origin: "omni-skills-private" source_repo: "diegosouzapw/awesome-omni-skills" replaces: - "core-web-vitals" --- # Core Web Vitals optimization ## Overview This public intake copy packages `packages/skills-catalog/skills/(performance)/core-web-vitals` from `https://github.com/tech-leads-club/agent-skills` into the native Omni Skills editorial shape without hiding its origin. Use it when the operator needs the upstream workflow, support files, and repository context to stay intact while the public validator and private enhancer continue their normal downstream flow. This intake keeps the copied upstream files intact and uses `metadata.json` plus `ORIGIN.md` as the provenance anchor for review. # Core Web Vitals optimization Targeted optimization for the three Core Web Vitals metrics that affect Google Search ranking and user experience. Imported source sections that did not map cleanly to the public headings are still preserved below or in the support files. Notable imported sections: The three metrics, LCP: Largest Contentful Paint, INP: Interaction to Next Paint, CLS: Cumulative Layout Shift, Measurement tools, Framework quick fixes. ## When to Use This Skill Use this section as the trigger filter. It should make the activation boundary explicit before the operator loads files, runs commands, or opens a pull request. - Use when the request clearly matches the imported source intent: Optimize Core Web Vitals (LCP, INP, CLS) for better page experience and search ranking. Use when asked to "improve Core Web Vitals", "fix LCP", "reduce CLS", "optimize INP", "page experience optimization", or "fix.... - Use when the operator should preserve upstream workflow detail instead of rewriting the process from scratch. - Use when provenance needs to stay visible in the answer, PR, or review packet. - Use when copied upstream references, examples, or scripts materially improve the answer. - Use when the workflow should remain reviewable in the public intake repo before the private enhancer takes over. ## Operating Table | Situation | Start here | Why it matters | | --- | --- | --- | | First-time use | `metadata.json` | Confirms repository, branch, commit, and imported path before touching the copied workflow | | Provenance review | `ORIGIN.md` | Gives reviewers a plain-language audit trail for the imported source | | Workflow execution | `references/LCP.md` | Starts with the smallest copied file that materially changes execution | | Supporting context | `references/LCP.md` | Adds the next most relevant copied source file without loading the entire package | | Handoff decision | `## Related Skills` | Helps the operator switch to a stronger native skill when the task drifts | ## Workflow This workflow is intentionally editorial and operational at the same time. It keeps the imported source useful to the operator while still satisfying the public intake standards that feed the downstream enhancer flow. 1. Confirm the user goal, the scope of the imported workflow, and whether this skill is still the right router for the task. 2. Read the overview and provenance files before loading any copied upstream support files. 3. Load only the references, examples, prompts, or scripts that materially change the outcome for the current request. 4. Execute the upstream workflow while keeping provenance and source boundaries explicit in the working notes. 5. Validate the result against the upstream expectations and the evidence you can point to in the copied files. 6. Escalate or hand off to a related skill when the work moves out of this imported workflow's center of gravity. 7. Before merge or closure, record what was used, what changed, and what the reviewer still needs to verify. ### Imported Workflow Notes #### Imported: 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. --- ## Examples ### Example 1: Ask for the upstream workflow directly ```text Use @core-web-vitals to handle . Start from the copied upstream workflow, load only the files that change the outcome, and keep provenance visible in the answer. ``` **Explanation:** This is the safest starting point when the operator needs the imported workflow, but not the entire repository. ### Example 2: Ask for a provenance-grounded review ```text Review @core-web-vitals against metadata.json and ORIGIN.md, then explain which copied upstream files you would load first and why. ``` **Explanation:** Use this before review or troubleshooting when you need a precise, auditable explanation of origin and file selection. ### Example 3: Narrow the copied support files before execution ```text Use @core-web-vitals for . Load only the copied references, examples, or scripts that change the outcome, and name the files explicitly before proceeding. ``` **Explanation:** This keeps the skill aligned with progressive disclosure instead of loading the whole copied package by default. ### Example 4: Build a reviewer packet ```text Review @core-web-vitals using the copied upstream files plus provenance, then summarize any gaps before merge. ``` **Explanation:** This is useful when the PR is waiting for human review and you want a repeatable audit packet. ## Best Practices Treat the generated public skill as a reviewable packaging layer around the upstream repository. The goal is to keep provenance explicit and load only the copied source material that materially improves execution. - Keep the imported skill grounded in the upstream repository; do not invent steps that the source material cannot support. - Prefer the smallest useful set of support files so the workflow stays auditable and fast to review. - Keep provenance, source commit, and imported file paths visible in notes and PR descriptions. - Point directly at the copied upstream files that justify the workflow instead of relying on generic review boilerplate. - Treat generated examples as scaffolding; adapt them to the concrete task before execution. - Route to a stronger native skill when architecture, debugging, design, or security concerns become dominant. ## Troubleshooting ### Problem: The operator skipped the imported context and answered too generically **Symptoms:** The result ignores the upstream workflow in `packages/skills-catalog/skills/(performance)/core-web-vitals`, fails to mention provenance, or does not use any copied source files at all. **Solution:** Re-open `metadata.json`, `ORIGIN.md`, and the most relevant copied upstream files. Load only the files that materially change the answer, then restate the provenance before continuing. ### Problem: The imported workflow feels incomplete during review **Symptoms:** Reviewers can see the generated `SKILL.md`, but they cannot quickly tell which references, examples, or scripts matter for the current task. **Solution:** Point at the exact copied references, examples, scripts, or assets that justify the path you took. If the gap is still real, record it in the PR instead of hiding it. ### Problem: The task drifted into a different specialization **Symptoms:** The imported skill starts in the right place, but the work turns into debugging, architecture, design, security, or release orchestration that a native skill handles better. **Solution:** Use the related skills section to hand off deliberately. Keep the imported provenance visible so the next skill inherits the right context instead of starting blind. ## Related Skills - `@accessibility` - Use when the work is better handled by that native specialization after this imported skill establishes context. - `@ai-cold-outreach` - Use when the work is better handled by that native specialization after this imported skill establishes context. - `@ai-pricing` - Use when the work is better handled by that native specialization after this imported skill establishes context. - `@ai-sdr` - Use when the work is better handled by that native specialization after this imported skill establishes context. ## Additional Resources Use this support matrix and the linked files below as the operator packet for this imported skill. They should reflect real copied source material, not generic scaffolding. | Resource family | What it gives the reviewer | Example path | | --- | --- | --- | | `references` | copied reference notes, guides, or background material from upstream | `references/LCP.md` | | `examples` | worked examples or reusable prompts copied from upstream | `examples/n/a` | | `scripts` | upstream helper scripts that change execution or validation | `scripts/n/a` | | `agents` | routing or delegation notes that are genuinely part of the imported package | `agents/n/a` | | `assets` | supporting assets or schemas copied from the source package | `assets/n/a` | - [LCP.md](references/LCP.md) - [LCP.md](references/LCP.md) ### Imported Reference Notes #### Imported: References - [web.dev LCP](https://web.dev/articles/lcp) - [web.dev INP](https://web.dev/articles/inp) - [web.dev CLS](https://web.dev/articles/cls) - [Performance skill](../performance/SKILL.md) #### Imported: 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 - `` element ### Common LCP issues **1. Slow server response (TTFB > 800ms)** ``` Fix: CDN, caching, optimized backend, edge rendering ``` **2. Render-blocking resources** ```html ``` **3. Slow resource load times** ```html Hero Hero ``` **4. Client-side rendering delays** ```javascript // ❌ 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 ```markdown - [ ] 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 - [ ] Fonts don't block text rendering (font-display: swap) - [ ] LCP element in initial HTML (not JS-rendered) ``` ### LCP element identification ```javascript // 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 }) ``` --- #### Imported: 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** ```javascript // ❌ 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** ```javascript // ❌ 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 requestIdleCallback for analytics requestIdleCallback(() => trackEvent('click')) }) ``` **3. Third-party scripts** ```javascript // ❌ Eagerly loaded, blocks interactions ; // ✅ Lazy loaded on interaction or visibility const loadWidget = () => { import('https://heavy-widget.com/widget.js').then((widget) => widget.init()) } button.addEventListener('click', loadWidget, { once: true }) ``` **4. Excessive re-renders (React/Vue)** ```javascript // ❌ Re-renders entire tree function App() { const [count, setCount] = useState(0) return (
{/* Re-renders on every count change */}
) } // ✅ Memoized expensive components const MemoizedExpensive = React.memo(ExpensiveComponent) function App() { const [count, setCount] = useState(0) return (
) } ``` ### INP optimization checklist ```markdown - [ ] No tasks > 50ms on main thread - [ ] Event handlers complete quickly (< 100ms) - [ ] Visual feedback provided immediately - [ ] Heavy work deferred with requestIdleCallback - [ ] Third-party scripts don't block interactions - [ ] Debounced input handlers where appropriate - [ ] Web Workers for CPU-intensive operations ``` ### INP debugging ```javascript // Identify slow interactions new PerformanceObserver((list) => { for (const entry of list.getEntries()) { if (entry.duration > 200) { console.warn('Slow interaction:', { type: entry.name, duration: entry.duration, processingStart: entry.processingStart, processingEnd: entry.processingEnd, target: entry.target, }) } } }).observe({ type: 'event', buffered: true, durationThreshold: 16 }) ``` --- #### Imported: CLS: Cumulative Layout Shift CLS measures unexpected layout shifts. A shift occurs when a visible element changes position between frames without user interaction. **CLS Formula:** `impact fraction × distance fraction` ### Common CLS causes **1. Images without dimensions** ```html Photo Photo Photo ``` **2. Ads, embeds, and iframes** ```html
``` **3. Dynamically injected content** ```javascript // ❌ Inserts content above viewport notifications.prepend(newNotification) // ✅ Insert below viewport or use transform const insertBelow = viewport.bottom < newNotification.top if (insertBelow) { notifications.prepend(newNotification) } else { // Animate in without shifting newNotification.style.transform = 'translateY(-100%)' notifications.prepend(newNotification) requestAnimationFrame(() => { newNotification.style.transform = '' }) } ``` **4. Web fonts causing FOUT** ```css /* ❌ Font swap shifts text */ @font-face { font-family: 'Custom'; src: url('custom.woff2') format('woff2'); } /* ✅ Optional font (no shift if slow) */ @font-face { font-family: 'Custom'; src: url('custom.woff2') format('woff2'); font-display: optional; } /* ✅ Or match fallback metrics */ @font-face { font-family: 'Custom'; src: url('custom.woff2') format('woff2'); font-display: swap; size-adjust: 105%; /* Match fallback size */ ascent-override: 95%; descent-override: 20%; } ``` **5. Animations triggering layout** ```css /* ❌ Animates layout properties */ .animate { transition: height 0.3s, width 0.3s; } /* ✅ Use transform instead */ .animate { transition: transform 0.3s; } .animate.expanded { transform: scale(1.2); } ``` ### CLS optimization checklist ```markdown - [ ] All images have width/height or aspect-ratio - [ ] All videos/embeds have reserved space - [ ] Ads have min-height containers - [ ] Fonts use font-display: optional or matched metrics - [ ] Dynamic content inserted below viewport - [ ] Animations use transform/opacity only - [ ] No content injected above existing content ``` ### CLS debugging ```javascript // Track layout shifts new PerformanceObserver((list) => { for (const entry of list.getEntries()) { if (!entry.hadRecentInput) { console.log('Layout shift:', entry.value) entry.sources?.forEach((source) => { console.log(' Shifted element:', source.node) console.log(' Previous rect:', source.previousRect) console.log(' Current rect:', source.currentRect) }) } } }).observe({ type: 'layout-shift', buffered: true }) ``` --- #### Imported: Measurement tools ### Lab testing - **Chrome DevTools** → Performance panel, Lighthouse - **WebPageTest** → Detailed waterfall, filmstrip - **Lighthouse CLI** → `npx lighthouse ` ### Field data (real users) - **Chrome User Experience Report (CrUX)** → BigQuery or API - **Search Console** → Core Web Vitals report - **web-vitals library** → Send to your analytics ```javascript import { onLCP, onINP, onCLS } from 'web-vitals' function sendToAnalytics({ name, value, rating }) { gtag('event', name, { event_category: 'Web Vitals', value: Math.round(name === 'CLS' ? value * 1000 : value), event_label: rating, }) } onLCP(sendToAnalytics) onINP(sendToAnalytics) onCLS(sendToAnalytics) ``` --- #### Imported: Framework quick fixes ### Next.js ```jsx // LCP: Use next/image with priority import Image from 'next/image' ;Hero // INP: Use dynamic imports const HeavyComponent = dynamic(() => import('./Heavy'), { ssr: false }) // CLS: Image component handles dimensions automatically ``` ### React ```jsx // LCP: Preload in head ; // INP: Memoize and useTransition const [isPending, startTransition] = useTransition() startTransition(() => setExpensiveState(newValue)) // CLS: Always specify dimensions in img tags ``` ### Vue/Nuxt ```vue ```