Borrowing it
Nothing to install: this file belongs to Piyush8296/claude-workspace. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/Piyush8296/claude-workspace/main/.claude/skills/core-web-vitals/SKILL.mdgit clone --depth 1 https://github.com/Piyush8296/claude-workspaceWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/piyush8296/claude-workspace/core-web-vitals)<a href="https://agentmods.dev/skills/piyush8296/claude-workspace/core-web-vitals"><img src="https://agentmods.dev/badge/skills/piyush8296/claude-workspace/core-web-vitals/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/piyush8296/claude-workspace/core-web-vitals"><img src="https://agentmods.dev/badge/skills/piyush8296/claude-workspace/core-web-vitals.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00066 | $0.02160 |
| Opus 5 | $0.00033 | $0.01080 |
| Sonnet 5 | $0.00013 | $0.00432 |
| Haiku 4.5 | $0.00007 | $0.00216 |
Grade A, and why
core-web-vitals scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 305 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Core Web Vitals
The Three Metrics That Affect Search Ranking
| Metric | Measures | Good | Needs Work | Poor |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Loading speed | ≤ 2.5s | ≤ 4.0s | > 4.0s |
| INP (Interaction to Next Paint) | Responsiveness | ≤ 200ms | ≤ 500ms | > 500ms |
| CLS (Cumulative Layout Shift) | Visual stability | ≤ 0.1 | ≤ 0.25 | > 0.25 |
LCP — Largest Contentful Paint
What it measures: How fast the biggest visible element loads (hero image, headline, video poster).
Diagnosis
# Run Lighthouse to identify LCP element
npx lighthouse http://localhost:3000 --output=json --quiet | \
jq '.audits["largest-contentful-paint"]'
# Check which element is the LCP
npx lighthouse http://localhost:3000 --output=json --quiet | \
jq '.audits["largest-contentful-paint-element"].details'
Fix Recipes
Hero image is the LCP element:
// BEFORE: lazy-loaded hero (kills LCP)
<Image src="/hero.jpg" alt="..." loading="lazy" />
// AFTER: preloaded, priority hero
<Image
src="/hero.webp" // Modern format
alt="Product hero showing the dashboard"
width={1200}
height={600}
priority // Preloads in <head>
fetchPriority="high" // Browser fetch priority
sizes="100vw" // Full-width
placeholder="blur" // Instant placeholder
blurDataURL={heroBlurDataUrl} // Base64 blur
/>
Headline text is the LCP element:
/* Preload the heading font */
<link rel="preload" href="/fonts/heading.woff2" as="font" type="font/woff2" crossorigin />
@font-face {
font-family: 'Heading';
src: url('/fonts/heading.woff2') format('woff2');
font-display: swap; /* Show fallback immediately */
}
Server response is slow:
// Switch from SSR to SSG/ISR for static content
// app/products/[slug]/page.tsx
export const revalidate = 3600; // ISR: regenerate every hour
// Or generate at build time
export async function generateStaticParams() {
const products = await getAllProducts();
return products.map((p) => ({ slug: p.slug }));
}
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 10d ago First seen · 305 lines · 66 tokens per session scan A a949c90e599c
core-web-vitals is a skill published in the GitHub repository Piyush8296/claude-workspace (2 stars, last pushed 4mo ago), licensed MIT. It adds 66 tokens to every session and 2,160 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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