
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.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/calm-north/seojuice-skills --skill audit-speed- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads audit-speed automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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:
- Which pages? Homepage, key landing pages, or specific slow pages.
- Current scores. If the user has Lighthouse or PageSpeed Insights data, start there.
- Tech stack. CMS, framework, hosting — this determines which optimizations are available.
- 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/heightattributes, usefetchpriority="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: swaporoptional, 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
widthandheightattributes to all<img>and<video>elements, use CSSaspect-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-sizefor 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
requestIdleCallbackorsetTimeout, 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:
-
[Metric]: [Root cause]
- Current: [value]
- Target: [threshold]
- Fix: [specific action]
- Estimated impact: [high/medium/low]
-
...
Quick Wins List optimizations that require minimal effort:
- Add
width/heightto 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.
FAQ
What does the audit-speed skill do?
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.
How do I install audit-speed?
Run npx skills add https://github.com/calm-north/seojuice-skills --skill audit-speed in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/audit-speed/ (personal) or .claude/skills/audit-speed/ (project).
Which AI agents can use audit-speed?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is audit-speed safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains audit-speed?
It is published by calm-north in calm-north/seojuice-skills. It has 2,406 recorded installs.
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