core-web-vitals

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 dalroot/agentic-seo --skill core-web-vitals

Clone the repo

git clone --depth 1 https://github.com/dalroot/agentic-seo

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/dalroot/agentic-seo/core-web-vitals/github.svg)](https://agentmods.dev/skills/dalroot/agentic-seo/core-web-vitals)

Your own site

<a href="https://agentmods.dev/skills/dalroot/agentic-seo/core-web-vitals"><img src="https://agentmods.dev/badge/skills/dalroot/agentic-seo/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/dalroot/agentic-seo/core-web-vitals"><img src="https://agentmods.dev/badge/skills/dalroot/agentic-seo/core-web-vitals.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 99 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 1,182 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 unknown 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.

Model	Per session	Once invoked
Fable 5.1	$0.00099	$0.01182
Opus 5.5	$0.00040	$0.00473
Sonnet 5.5	$0.00020	$0.00236
Haiku 4.5	$0.00010	$0.00118

Measured today against content hash 7ab585fda04d, 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 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 today.

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/seo/technical/core-web-vitals/SKILL.md · 98 lines

How it starts

The opening of the file, as written. The whole thing — 98 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SEO Technical: Core Web Vitals

Guides optimization of Core Web Vitals (CWV)—Google's user experience metrics that affect search ranking. CWV are confirmed ranking factors for mobile and desktop.

When invoking: On first use, if helpful, open with 1–2 sentences on what this skill covers and why it matters, then provide the main output. On subsequent use or when the user asks to skip, go directly to the main output.

Scope (Technical SEO)

LCP (Largest Contentful Paint): Loading performance; time to render largest content element
INP (Interaction to Next Paint): Responsiveness; replaced FID on March 12, 2024
CLS (Cumulative Layout Shift): Visual stability; unexpected layout shifts

Target Thresholds (75th percentile, field data)

Metric	Target	Good	Needs Improvement	Poor
LCP	≤2.5s	≤2.5s	2.5–4.0s	>4.0s
INP	≤200ms	≤200ms	200–500ms	>500ms
CLS	<0.1	≤0.1	0.1–0.25	>0.25

Source: Google Page Experience

Initial Assessment

Check for project context first: If .claude/project-context.md or .cursor/project-context.md exists, read it for site URL.

Identify:

Tools: GSC Core Web Vitals report, PageSpeed Insights, Chrome DevTools
Metrics: Which metric is failing (LCP, INP, CLS)
Page type: Hero, article, product, list—LCP candidate differs

LCP Optimization

LCP measures the time until the largest content element (image, video, or text block) is visible.

Cause	Fix
Slow server response	Reduce TTFB; use CDN; optimize server
Render-blocking resources	Defer non-critical CSS/JS; inline critical CSS
Large images	WebP/AVIF; compress; `width`/`height` to prevent CLS; see image-optimization
Client-side rendering	SSR/SSG for above-fold content; see rendering-strategies
Third-party scripts	Load async; defer non-critical

Read the full file on GitHub · 98 lines

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.

today First seen · 98 lines · 99 tokens per session scan A 7ab585fda04d

Subscribe to this mod's changes

core-web-vitals is a skill published in the GitHub repository dalroot/agentic-seo (25 stars, last pushed 6d ago), licensed MIT. It adds 99 tokens to every session and 1,182 once invoked, about $0.0004 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 2026-10-26.

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