# Webpagetest

> Use when reviewing templates, rendered HTML, or shared components related to Analyze performance with WebPageTest. Validate the final browser-facing markup, not just the source framework abstraction.

- Skill: `thedaviddias/webpagetest` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add thedaviddias/webpagetest`
- Raw SKILL.md: https://api.skillmd.com/api/skills/thedaviddias/webpagetest/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: thedaviddias (https://skillmd.com/u/thedaviddias)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/thedaviddias/webpagetest

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# Analyze performance with WebPageTest

WebPageTest reveals real-world performance issues that synthetic tools miss—like TTFB from actual locations, render-blocking patterns, and third-party script impact.

## Quick Reference

- Run 3+ tests to get consistent results
- Test from locations near your users
- Use filmstrip view to identify visual progress
- Check waterfall for blocking resources and slow third-parties

## Check

Use WebPageTest to analyze page performance, identify bottlenecks, and measure real-world loading metrics across different devices and connections.

## Fix

Implement recommended optimizations from WebPageTest results including resource compression, caching, and critical path improvements.

## Explain

Explain how WebPageTest provides insights into Core Web Vitals, loading waterfalls, and performance opportunities that synthetic testing can't reveal.

## Code Review

Review templates, server-rendered HTML, and shared components that output markup related to Analyze performance with WebPageTest. Flag exact elements, attributes, and routes where the rendered HTML violates the rule.

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For full implementation details, code examples, and framework-specific guidance,
see `references/rule.md`.

Rule page: https://frontendchecklist.io/en/rules/html/webpagetest