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Core Web Vitals Optimization

Diagnose and fix LCP, INP, and CLS using real-user CrUX field data plus browser performance traces.

Dev & CodingIntermediate★ 2,875⑂ 253AI score 9/10Last updated: Aug 24, 2026

What it does

  • Evaluates the three Core Web Vitals (LCP for loading, INP for responsiveness, CLS for visual stability) against p75 thresholds and proposes targeted fixes.
  • Enforces a measure-first workflow: page-level CrUX field data → browser performance trace → analyze only the failing metric's insights → re-measure in equivalent lab conditions after the fix.
  • Gives concrete code fixes per LCP cause: slow TTFB, render-blocking CSS/JS, late-discovered hero images, client-side rendering delays — plus a full LCP checklist.
  • Covers the Speculation Rules API for instant navigations, including an eagerness trigger table, bandwidth caveats, early-firing side effects, and Chromium-only limits.
  • Defers deep INP and CLS work to dedicated reference docs, and includes quick fixes for Next.js, React, and Vue/Nuxt.

Who it's for

  • Frontend engineers, web performance owners, and SEO/page-experience teams.
  • Site owners hit with "Poor URLs" warnings in Search Console.
  • Teams with Chrome DevTools MCP or Lighthouse already available for measurement.

Example uses

  1. "Our product page LCP is 4s — find why" → checks CrUX, records a trace, pinpoints late hero-image discovery and recommends fetchpriority="high" plus WebP/AVIF.
  2. "Mobile layout keeps jumping (CLS 0.28)" → identifies the actually shifted node and trigger, then applies reserved space, font-display: swap, and banner slot patterns.
  3. "Button taps feel laggy (INP 480ms)" → separates input delay, processing time, and presentation delay, then suggests yielding and deferring third-party scripts.

· · · Install guide · · ·

Try it now, no install

Paste this into Claude to use the skill without installing anything.

Read the instructions in this file and follow them to help me:
https://raw.githubusercontent.com/addyosmani/web-quality-skills/HEAD/skills/core-web-vitals/SKILL.md

What I want: (describe your task here)

If Claude can't open the link, open it yourself and paste the contents instead.

↓ If it works for you, download the ZIP below and install it. Then it runs on its own — no pasting each time.

Install in the Claude app (no terminal)
  1. Download the ZIP with the button below.
  2. In Claude, open Settings → Capabilities and turn on 'Code execution and file creation'. (one time)
  3. Go to Customize → Skills → + → 'Upload a skill' and upload the ZIP.
↓ Download ZIP
Install in Claude Code

Let Claude do it — paste this into Claude Code

Install the skill I found on Claude Skill Mart.
Copy the skills/core-web-vitals folder from the GitHub repo addyosmani/web-quality-skills into my ~/.claude/skills/core-web-vitals/.
When it's done, tell me in one line what this skill can do.

Install with a command instead

git clone https://github.com/addyosmani/web-quality-skills.git && mkdir -p ~/.claude/skills && cp -r web-quality-skills/skills/* ~/.claude/skills/

⚠ This is a third-party skill. Check the source repository before installing.

  1. Open a terminal.
  2. Clone the repo: git clone https://github.com/addyosmani/web-quality-skills.git
  3. Create the skills folder: mkdir -p ~/.claude/skills
  4. Copy the skills over: cp -r web-quality-skills/skills/* ~/.claude/skills/ (copy all of them — this skill references ../performance/references/).
  5. Verify with ls ~/.claude/skills/core-web-vitals — you should see SKILL.md and a references folder.
  6. Restart Claude Code and ask something like "improve Core Web Vitals for my site".
  7. (Recommended) Connect Chrome DevTools MCP or install Lighthouse CLI (npm i -g lighthouse) and have a runnable URL ready so the skill can work from real measurements instead of guesses.
View source on GitHub ↗License: MIT