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calm-north/seojuice-skills

audit-speed

Deep Core Web Vitals and page speed audit. Use when the user asks about page speed, Core Web Vitals, LCP, CLS, INP, FCP, TTFB, Lighthouse scores, why a page is slow, performance optimization, or resource size analysis. For broader technical SEO issues, see diagnose-seo.

All-time #5468 First seen Feb 27, 2026
8-week activity · all time api

Installation

$ npx skills add calm-north/seojuice-skills --skill audit-speed
View on skills.sh ↗ GitHub repository ↗

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More details

Agent compatibility

Declared targets from SKILL.md / docs. Unmarked agents are not listed — the skill may still install via the CLI.

Claude Code Not declared
Cursor Not declared
Codex Not declared
GitHub Copilot Not declared
Windsurf Not declared
Gemini CLI Not declared
Cline Not declared
OpenCode Not declared

Repository health

Stars 21
License LICENSE
Default branch main
Open issues 0
Status Active

Skill metadata

Parsed from SKILL.md frontmatter.

Version1.0.0
More metadata
version
1.0.0

Package contents

Files included with this skill beyond the listing page.

  • skill md SKILL.md 6,154 B
  • docs SUMMARY.md 288 B

History

  1. First seen on skills.sh
  2. First recorded snapshot · 2,400 installs

SKILL.md

Audit Speed

Deep Core Web Vitals audit with root-cause analysis trees and resource optimization recommendations.

Core Web Vitals Thresholds

Metric Good Needs Improvement Poor
LCP (Largest Contentful Paint) < 2.5s 2.5s - 4.0s > 4.0s
CLS (Cumulative Layout Shift) < 0.1 0.1 - 0.25 > 0.25
INP (Interaction to Next Paint) < 200ms 200ms - 500ms > 500ms
FCP (First Contentful Paint) < 1.8s 1.8s - 3.0s > 3.0s
TTFB (Time to First Byte) < 800ms 800ms - 1800ms > 1800ms

Before You Start

Gather this context:

  1. Which pages? Homepage, key landing pages, or specific slow pages.
  2. Current scores. If the user has Lighthouse or PageSpeed Insights data, start there.
  3. Tech stack. CMS, framework, hosting — this determines which optimizations are available.
  4. Known constraints. Third-party scripts they can't remove, design requirements that limit optimization.

If no data is available, suggest running Google PageSpeed Insights on the key URLs.

LCP Root-Cause Tree

LCP measures when the largest visible element finishes rendering. Diagnose:

Is TTFB slow (> 800ms)?

  • → Server response time issue
  • Check: hosting quality, CDN configuration, database queries, server-side rendering time
  • Fix: upgrade hosting, add CDN, optimize server-side code, enable caching

Is the LCP element an image?

  • → Image optimization issue
  • Check: image format (use WebP/AVIF), image size (serve responsive sizes), lazy loading on LCP image (should NOT be lazy loaded)
  • Fix: convert to modern formats, add width/height attributes, use fetchpriority="high" on LCP image, preload the LCP image

Is the LCP element text?

  • → Font loading issue
  • Check: custom fonts blocking render, font file size, font-display strategy
  • Fix: use font-display: swap or optional, preload critical fonts, subset fonts to used characters

Is render-blocking CSS/JS delaying the LCP?

  • Check: large CSS files in <head>, synchronous JS before content
  • Fix: inline critical CSS, defer non-critical CSS, async/defer JS

CLS Root-Cause Tree

CLS measures unexpected layout shifts. Diagnose:

Do images/videos lack dimensions?

  • → Browser can't reserve space before loading
  • Fix: add width and height attributes to all <img> and <video> elements, use CSS aspect-ratio

Do ads or embeds inject content?

  • → Dynamic content pushing existing content down
  • Fix: reserve space for ad slots with min-height, use contain-intrinsic-size for lazy content

Do fonts cause text reflow?

  • → FOUT (Flash of Unstyled Text) causes layout shift when custom font loads
  • Fix: use font-display: optional (no swap = no shift), or match fallback font metrics

Does dynamic content insert above the fold?

  • → Banners, cookie notices, notifications pushing content
  • Fix: use overlays instead of inline insertions, or reserve space with fixed-height containers

INP Root-Cause Tree

INP measures responsiveness to user interactions. Diagnose:

Is the main thread blocked by long tasks?

  • Check: JavaScript execution time, third-party scripts, large DOM
  • Fix: break long tasks with requestIdleCallback or setTimeout, code-split heavy modules

Do event handlers do heavy synchronous work?

  • Check: click handlers that trigger large DOM updates, form validation on every keystroke
  • Fix: debounce inputs, use requestAnimationFrame for visual updates, offload work to web workers

Are third-party scripts competing for the main thread?

  • Check: analytics, chat widgets, A/B testing tools, social embeds
  • Fix: defer loading until after interaction, use loading="lazy" for embeds, consider removing low-value scripts

Resource Analysis

Break down the total page weight:

Resource Type Size Assessment Action
HTML [x] KB [ok/large] Compress, reduce inline styles/scripts
CSS [x] KB [ok/large] Remove unused CSS, minify, critical CSS extraction
JavaScript [x] KB [ok/large] Code-split, tree-shake, defer non-critical
Images [x] KB [ok/large] Modern formats, responsive sizes, lazy load below fold
Fonts [x] KB [ok/large] Subset, limit families/weights, preload critical
Third-party [x] KB [ok/large] Audit necessity, defer, self-host if possible

Benchmarks:

  • Total page weight under 1.5 MB is good
  • JavaScript under 300 KB (compressed) for most sites
  • CSS under 100 KB (compressed)
  • First-party fonts under 100 KB

Output Format

Speed Audit: [URL or domain]

Core Web Vitals

Metric Value Rating Root Cause
LCP [value] Good / Needs Improvement / Poor [identified cause]
CLS [value] ... ...
INP [value] ... ...
FCP [value] ... ...
TTFB [value] ... ...

Resource Breakdown [Table from Resource Analysis]

Priority Fixes

For each failing metric, ordered by impact:

  1. [Metric]: [Root cause]

- Current: [value] - Target: [threshold] - Fix: [specific action] - Estimated impact: [high/medium/low]

  1. ...

Quick Wins List optimizations that require minimal effort:

  • Add width/height to images
  • Set fetchpriority="high" on LCP image
  • Defer non-critical JavaScript
  • ...

Pro Tip: Use the free CWV Impact Calculator
to estimate the traffic impact of fixing Core Web Vitals, and the
Critical CSS Generator to extract
above-the-fold CSS. SEOJuice MCP users can run /seojuice:page-audit [domain] [url] for
instant CWV scores, Lighthouse data, and resource breakdowns.