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.
npx skills add JakeLabate/Claude-SEO-Skills --skill core-web-vitals-auditgit clone --depth 1 https://github.com/JakeLabate/Claude-SEO-SkillsWrote 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/jakelabate/claude-seo-skills/core-web-vitals-audit)<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.
<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>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 | $0.00133 | $0.01998 |
| Opus 5 | $0.00067 | $0.00999 |
| Sonnet 5 | $0.00027 | $0.00400 |
| Haiku 4.5 | $0.00013 | $0.00200 |
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 11d 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 — 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:
- 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.
- 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:
- 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. - Scope — max pages (default 50; collection is heavier than a text crawl because it fetches subresources).
- PSI — whether to fetch PageSpeed Insights field data (
--psi), the strategy (mobiledefault, ordesktop), and an optional API key (--psi-key) to raise rate limits. - Budgets — optional overrides for total page weight, TTFB, JS/CSS size, and DOM node count.
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.
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.
- 11d ago First seen · 139 lines · 133 tokens per session scan A ea985a1466ba
core-web-vitals-audit is a skill published in the GitHub repository JakeLabate/Claude-SEO-Skills (2 stars, last pushed 2mo ago), licensed MIT. It adds 133 tokens to every session and 1,998 once invoked, about $0.0007 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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