Is the Core Web Vitals skill free?

Yes. The skill itself is free from addyosmani/web-quality-skills. SkillProof publishes the install command and an independent test verdict at no cost.

What is the Core Web Vitals SkillProof Score?

9.2/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 8/10, docs & honesty 5/5.

How do I install Core Web Vitals?

Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.

Can I use Core Web Vitals with Cursor, Copilot, Gemini CLI, Codex or other AI tools?

The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.

Core Web Vitals

Actionable LCP/INP/CLS fixes with modern APIs (fetchpriority, scheduler.yield, Speculation Rules)

by addyosmani · addyosmani/web-quality-skills

Tested · Works

Install — copy the command Download source ↗

Test report

Verdict: Tested · Works
Score: 9.2/10
Tested: Jul 20, 2026
Environment: Claude Code 2.x (agent harness)
Upstream re-checked: Aug 10, 2026 · 5c8fa06

Fetched the repo tree (6 SKILL.md files under skills/; picked skills/core-web-vitals/SKILL.md by slug match) and read the raw file fully. Frontmatter parses with name+description; the only local link (../performance/SKILL.md) exists in the tree, all other links are external web.dev docs; no scripts, no exfiltration/base64/hidden instructions, pure Markdown instructions. Content is current and specific — fetchpriority="high", scheduler.yield() with Safari fallback, Speculation Rules prerender with side-effect caveats, font-display + size-adjust for CLS.

Scored on four weighted criteria — install, triggering, output vs. baseline, docs. How scoring works

Installs cleanly 5/5
Triggers reliably 5/5
Output vs. baseline 8/10
Docs & honesty 5/5

What Core Web Vitals does

A single-file prompt skill that guides Claude to diagnose and fix the three Core Web Vitals — LCP, INP, and CLS — with concrete before/after code, per-metric checklists, and framework quick-fixes (Next.js/React/Vue). Triggers on phrasings like "improve Core Web Vitals", "fix LCP", "reduce CLS", or "optimize INP". Self-contained, no external tooling required to apply its advice.

How to install Core Web Vitals

Copy the skill folder into your Claude skills dir: git clone https://github.com/addyosmani/web-quality-skills && cp -r web-quality-skills/skills/core-web-vitals ~/.claude/skills/core-web-vitals

Skills live in ~/.claude/skills/ (global) or .claude/skills/ (per-project). Restart Claude Code after installing.

Commands — how to trigger Core Web Vitals

/core-web-vitals Actionable LCP/INP/CLS fixes with modern APIs (fetchpriority, scheduler.yield, Speculation Rules)

It also activates on plain-language prompts like these:

Improve my site's Core Web Vitals scores
Fix the layout shift causing a high CLS
Reduce the LCP score on our homepage

Frequently asked questions

Is the Core Web Vitals skill free?: Yes. The skill itself is free from addyosmani/web-quality-skills. SkillProof publishes the install command and an independent test verdict at no cost.
Does Core Web Vitals work with Claude Code?: We tested it with Claude Code 2.x (agent harness) on Jul 20, 2026. Verdict: Tested · Works. Fetched the repo tree (6 SKILL.md files under skills/; picked skills/core-web-vitals/SKILL.md by slug match) and read the raw file fully. Frontmatter parses with name+description; the only local link (../performance/SKILL.md) exists in the tree, all other links are external web.dev docs; no scripts, no exfiltration/base64/hidden instructions, pure Markdown instructions. Content is current and specific — fetchpriority="high", scheduler.yield() with Safari fallback, Speculation Rules prerender with side-effect caveats, font-display + size-adjust for CLS.
What is the Core Web Vitals SkillProof Score?: 9.2/10 — installs cleanly 5/5, triggers reliably 5/5, output vs. baseline 8/10, docs & honesty 5/5.
How do I install Core Web Vitals?: Copy the install command from this page, run it in your terminal, and restart Claude Code. Skills live in ~/.claude/skills/ (global) or .claude/skills/ inside a project.
Can I use Core Web Vitals with Cursor, Copilot, Gemini CLI, Codex or other AI tools?: The SKILL.md format is native to Claude (Claude Code, Desktop, claude.ai). The instructions inside adapt to other assistants: Cursor rules, GitHub Copilot instructions, Windsurf rules, Custom GPTs, AGENTS.md for OpenAI Codex, and GEMINI.md for Google Gemini CLI — our conversion guides cover each, and the free converter on the tools page does the wrapping for you.