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core-web-vitals-audit

core-web-vitals-audit is a skill for Claude Code, Codex from JakeLabate/Claude-SEO-Skills. It costs 133 tokens per session (1,998 once invoked), scanned A, original, MIT.

A website performance review covering loading speed, visual movement during loading, interaction response, server response time, and related page signals. Core Web Vitals are Google's measures of real-world website loading and usability.

In plain words
What is it for?
Use it to inspect LCP, CLS, INP, and TTFB, page weight, browser requests, render-blocking CSS and JavaScript, image loading, compression, DOM size, and third-party resources.
Why use it?
It identifies likely causes of slow or unstable pages, such as blocking files, oversized images, large pages, slow servers, or missing image dimensions. It can also compare lab measurements with real-user data from Google's services.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

not rated 3repo 4mo ago A scan 133 tokens original MIT

Good fit Use it to inspect LCP, CLS, INP, and TTFB, page weight, browser requests, render-blocking CSS and JavaScript, image loading, compression, DOM size, and third-party resources.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jakelabate/claude-seo-skills/core-web-vitals-audit
View source ↗ JakeLabate/Claude-SEO-Skills jakelabate.com
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add JakeLabate/Claude-SEO-Skills --skill core-web-vitals-audit
Clone the repo
git clone --depth 1 https://github.com/JakeLabate/Claude-SEO-Skills

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for core-web-vitals-audit

README.md
[![agentmods](https://agentmods.dev/badge/skills/jakelabate/claude-seo-skills/core-web-vitals-audit/github.svg)](https://agentmods.dev/skills/jakelabate/claude-seo-skills/core-web-vitals-audit)
Your own site
<a href="https://agentmods.dev/skills/jakelabate/claude-seo-skills/core-web-vitals-audit"><img src="https://agentmods.dev/badge/skills/jakelabate/claude-seo-skills/core-web-vitals-audit/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.

agentmods 80×15 button for core-web-vitals-audit

Your own site · 80×15
<a href="https://agentmods.dev/skills/jakelabate/claude-seo-skills/core-web-vitals-audit"><img src="https://agentmods.dev/badge/skills/jakelabate/claude-seo-skills/core-web-vitals-audit.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 133 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,998 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00133 $0.01998
Opus 5.5 $0.00053 $0.00799
Sonnet 5.5 $0.00027 $0.00400
Haiku 4.5 $0.00013 $0.00200

Measured 2mo ago against content hash ea985a1466ba, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

core-web-vitals-audit 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 2mo ago.

The scan reads SKILL.md. This mod also ships 4 executable files (scripts/audit_vitals.py, scripts/collect_vitals.py, scripts/findings_to_csv.py, …), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/core-web-vitals-audit/SKILL.md · 139 lines

How it starts

The opening of the file, as written. The whole thing — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Core Web Vitals Audit

Audit the Core Web Vitals and page-experience signals of a website and produce an actionable report.

When to use this skill

Use this skill when the user asks to:

  • Audit or improve Core Web Vitals, page speed, or page experience
  • Diagnose poor LCP (Largest Contentful Paint), CLS (Cumulative Layout Shift), or INP (Interaction to Next Paint)
  • Find render-blocking resources, oversized pages, slow TTFB, or layout-shift causes
  • Check that images have dimensions and that the hero/LCP image is not lazy-loaded
  • Pull real-world field performance data from Google PageSpeed Insights / CrUX

How this skill measures

Core Web Vitals are ultimately a field metric (real users, measured in CrUX). This skill collects two complementary layers:

  1. Lab proxies (always, no browser required): static signals that strongly correlate with the vitals — measured TTFB, page weight, render-blocking CSS/JS, image dimension/lazy-loading hygiene, DOM size, request counts, third-party origins, text compression, and resource hints. Fast and dependency-free, but an approximation.
  2. PSI field + lab (optional, --psi): real CrUX field metrics (LCP, CLS, INP, FCP, TTFB) plus a Lighthouse lab score from Google PageSpeed Insights. This is the authoritative source; use it when you need real numbers and have network access.

When PSI data is present, treat it as the verdict ("is this page passing?") and use the lab proxies to explain why and what to fix.

Inputs to collect

Before starting, confirm with the user:

  1. Site URL or URL set — a live site root URL, a sitemap (--sitemap), or a URL list (--url-list). Pick representative templates (home, a product/article, a category) rather than the whole site.
  2. Scope — max pages (default 50; collection is heavier than a text crawl because it fetches subresources).
  3. PSI — whether to fetch PageSpeed Insights field data (--psi), the strategy (mobile default, or desktop), and an optional API key (--psi-key) to raise rate limits.
  4. Budgets — optional overrides for total page weight, TTFB, JS/CSS size, and DOM node count.

Read the full file on GitHub · 139 lines

Files

What ships with it

6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

  1. 2mo ago First seen · 139 lines · 133 tokens per session scan A ea985a1466ba

Subscribe to this mod's changes

core-web-vitals-audit is a skill published in the GitHub repository JakeLabate/Claude-SEO-Skills (3 stars, last pushed 4mo ago), licensed MIT. It adds 133 tokens to every session and 1,998 once invoked, about $0.0005 per session on Opus 5.5. 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.

Analytics and metricsaeoaiaiseoclaudegeoschema-org
Related

core-web-vitals-audit compared with skills from other repositories

core-web-vitals-audit next to 6 skills from other repositories
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core-web-vitals-auditJakeLabate/Claude-SEO-SkillsSkill34mo agoMITA133Claude Code, Codex
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audit-contentonvoyage-ai/gtm-engineer-skillsSkill1.4k27d agoMITA40Claude Code, Codex