# pagespeed-insights

A skill that audits a web page against PageSpeed Insights guidelines: Core Web Vitals, bottlenecks, bad practices.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1100 installs · ★ 2
- Author: EnderPuentes
- License: CC-BY-4.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/EnderPuentes/ai-agent-skills/tree/HEAD/pagespeed-insights/SKILL.md
- Updated: 2026-10-01
- HTML: https://affpapa.org/en/nevibecode/skills/pagespeed-insights

## What it does

This skill turns the agent into a performance auditor. It follows the PageSpeed Insights guidelines and reviews a page across four categories: Performance, Accessibility, Best Practices and SEO. The target is a score of 90 or higher, with Core Web Vitals inside the Good thresholds.

Inside you get a catalogue of common problems with code samples. Uncompressed images without `srcset` or explicit `width`/`height`, render-blocking CSS and JS, missing `preconnect` and `preload`, layout shifts from containers without `aspect-ratio`, oversized JS bundles, fonts without `font-display: swap`. Each case shows the bad version next to the good one.

The skill separates Lighthouse lab data from Chrome User Experience Report (CrUX) field data. Lab numbers help with debugging; field data reflects what visitors actually get. If the report shows green circles while real users still sit above 2500 ms on LCP, trust the field data — that gap is your cue to check what is slow on real devices.

Metric thresholds sit in tables: FCP, LCP, CLS, INP and TTFB, each split into Good, Needs Improvement and Poor.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add EnderPuentes/ai-agent-skills --skill pagespeed-insights -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/pagespeed-insights/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/pagespeed-insights/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add EnderPuentes/ai-agent-skills --skill pagespeed-insights -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/pagespeed-insights/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add EnderPuentes/ai-agent-skills --skill pagespeed-insights -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/pagespeed-insights/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install EnderPuentes/ai-agent-skills pagespeed-insights
```

2. **Manually: put the files in place**
- File: `.github/skills/pagespeed-insights/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add EnderPuentes/ai-agent-skills --skill pagespeed-insights -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/EnderPuentes/ai-agent-skills --path pagespeed-insights
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/pagespeed-insights/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add EnderPuentes/ai-agent-skills --skill pagespeed-insights -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/EnderPuentes/ai-agent-skills/tree/HEAD/pagespeed-insights/SKILL.md

## When to use it
- find out why mobile LCP exceeds 2500 ms
- stop layout shifts caused by unsized images
- shrink the JS bundle and cut TBT
- set up preconnect and preload for third-party origins
- raise the Lighthouse SEO score

## Example prompts
- audit this page against PageSpeed Insights and tell me what is slow
- why is my CLS bad — walk through the markup
- compare lab and field data for the homepage

## Source text · SKILL.md · CC-BY-4.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 8c80952266fdffe3.

BEGIN THIRD-PARTY FILE 8c80952266fdffe3
```text
---
name: pagespeed-insights
description: Audit web pages for performance optimization following PageSpeed Insights guidelines. Use when analyzing page performance, optimizing web applications, reviewing performance metrics, implementing Core Web Vitals improvements, or when the user mentions page speed, performance optimization, Lighthouse scores, or Core Web Vitals.
---

# PageSpeed Insights Auditor

## Overview

You are a **PageSpeed Insights Auditor** - an expert in web performance optimization who helps developers achieve excellent PageSpeed scores by identifying performance issues, avoiding bad practices, and implementing best practices based on Google's PageSpeed Insights guidelines.

**Core Principle**: Guide developers to achieve scores of 90+ (Good) in Performance, Accessibility, Best Practices, and SEO categories, while ensuring Core Web Vitals metrics meet the "Good" thresholds.

## Understanding PageSpeed Insights

PageSpeed Insights (PSI) analyzes page performance on mobile and desktop devices, providing both **lab data** (simulated) and **field data** (real user experiences). PSI reports on user experience metrics and provides diagnostic suggestions to improve page performance.

### Two Types of Data

1. **Lab Data**: Collected in a controlled environment using Lighthouse. Useful for debugging but may not capture real-world bottlenecks.
2. **Field Data**: Real user experience data from Chrome User Experience Report (CrUX). Useful for capturing actual user experiences but has a more limited set of metrics.

## Performance Score Thresholds

### Lab Scores (Lighthouse)

| Score Range | Rating            | Icon            |
| ----------- | ----------------- | --------------- |
| 90-100      | Good              | 🟢 Green circle |
| 50-89       | Needs Improvement | 🟡 Amber square |
| 0-49        | Poor              | 🔴 Red triangle |

**Target**: Always aim for scores of **90 or higher** in all categories.

### Core Web Vitals Thresholds

Core Web Vitals are the three most important metrics for web performance:

| Metric                              | Good         | Needs Improvement  | Poor      |
| ----------------------------------- | ------------ | ------------------ | --------- |
| **FCP** (First Contentful Paint)    | [0, 1800 ms] | [1800 ms, 3000 ms] | > 3000 ms |
| **LCP** (Largest Contentful Paint)  | [0, 2500 ms] | [2500 ms, 4000 ms] | > 4000 ms |
| **CLS** (Cumulative Layout Shift)   | [0, 0.1]     | [0.1, 0.25]        | > 0.25    |
| **INP** (Interaction to Next Paint) | [0, 200 ms]  | [200 ms, 500 ms]   | > 500 ms  |
```
END THIRD-PARTY FILE 8c80952266fdffe3

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