seo-performance

seo-performance is a skill for Claude Code, Codex from 01clauding/claude-seo-skill. It costs 86 tokens per session (1,648 once invoked), scanned A, original, MIT.

A website performance analysis focused on Core Web Vitals: loading speed, responsiveness to user actions, and visual stability. It also checks HTTP/3, Lighthouse scoring, field data, and the parts of a page that affect its main loading time.

In plain words
What is it for?
Use it to review LCP, INP, and CLS, check HTTP/3 support, inspect real-user performance data, and find the causes of slow main content loading.
Why use it?
It helps explain why a page feels slow, reacts late, or shifts as it loads. It combines lab checks with real-user data where available.

Skill for Claude CodeCodex

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

Good fit Use it to review LCP, INP, and CLS, check HTTP/3 support, inspect real-user performance data, and find the causes of slow main content loading.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/01clauding/claude-seo-skill/seo-performance
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 01clauding/claude-seo-skill --skill seo-performance
Clone the repo
git clone --depth 1 https://github.com/01clauding/claude-seo-skill

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 seo-performance

README.md
[![agentmods](https://agentmods.dev/badge/skills/01clauding/claude-seo-skill/seo-performance.svg)](https://agentmods.dev/skills/01clauding/claude-seo-skill/seo-performance)
Your own site
<a href="https://agentmods.dev/skills/01clauding/claude-seo-skill/seo-performance"><img src="https://agentmods.dev/badge/skills/01clauding/claude-seo-skill/seo-performance.svg" alt="Measured on agentmods" height="20"></a>
Per session 86 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,648 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 1 finding. 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 $0.00086 $0.01648
Opus 5 $0.00043 $0.00824
Sonnet 5 $0.00017 $0.00330
Haiku 4.5 $0.00009 $0.00165

Measured 8d ago against content hash 926de2da3be0, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

seo-performance scanned grade A with 1 finding 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 8d 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.

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl -sI --http3 https://example.com | grep -i "HTTP/3"
skills/seo-performance/SKILL.md · 156 lines

How it starts

The opening of the file, as written. The whole thing — 156 lines — stays where its author put it; the contents beside it link to each section on GitHub.

seo-performance — Core Web Vitals & Page Performance

Core Web Vitals Thresholds (2026)

Metric Good Needs Improvement Poor
LCP (Largest Contentful Paint) ≤2.5s 2.5s–4.0s >4.0s
INP (Interaction to Next Paint) ≤200ms 200ms–500ms >500ms
CLS (Cumulative Layout Shift) ≤0.1 0.1–0.25 >0.25

INP replaced FID on March 12, 2024. FID fully removed September 9, 2024. Never reference FID.

Key Statistics (2026)

  • 77% of mobile pages now achieve "good" INP (up from 55% in 2022)
  • 57.1% desktop / 49.7% mobile pass all three CWV (Oct 2025)
  • December 2025 core update: Mobile CWV weighted more heavily in ranking calculations
  • CWV evaluated at 75th percentile of field data — 75% of visits must meet "good"

HTTP/3 & QUIC Analysis

HTTP/3 reached 35% global adoption (2025), reducing mobile latency by 30%.

Check HTTP/3 Support

curl -sI --http3 https://example.com | grep -i "HTTP/3"
# Or check via headers:
curl -sI https://example.com | grep -i "alt-svc"

HTTP/3 Scoring

Status Score Recommendation
HTTP/3 enabled (Alt-Svc header present) 100 Excellent
HTTP/2 only 50 Enable HTTP/3 at CDN level (Cloudflare: default, AWS CloudFront: opt-in)
HTTP/1.1 0 Upgrade immediately — significant performance penalty

HTTP/3 is NOT a direct ranking factor but improves TTFB and LCP subparts measurably.

LCP Subpart Diagnostics (Feb 2025 CrUX Addition)

Break down LCP into 4 subparts for targeted optimization:

Subpart What It Measures Target
TTFB Server response time <800ms
Resource Load Delay Time before LCP resource starts loading Minimize (preload)
Resource Load Time Time to download LCP resource Compress, CDN, modern formats
Element Render Delay Time from resource loaded to rendered Reduce render-blocking CSS/JS

Read the full file on GitHub · 156 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.

  1. 8d ago First seen · 156 lines · 86 tokens per session scan A 926de2da3be0

Subscribe to this mod's changes

seo-performance is a skill published in the GitHub repository 01clauding/claude-seo-skill (4 stars, last pushed 5mo ago), licensed MIT. It adds 86 tokens to every session and 1,648 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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