Web Perf

---
name: web-perf
description: Analyzes web performance using Chrome DevTools MCP. Measures Core Web Vitals (LCP, INP, CLS) and supplementary metrics (FCP, TBT, Speed Index), identifies render-blocking resources, network dependency chains, layout shifts, caching issues, and accessibility gaps. Use when asked to audit, profile, debug, or optimize page load performance, Lighthouse scores, or site speed. Biases towards retrieval from current documentation over pre-trained knowledge.
---

# Web Performance Audit

Your knowledge of web performance metrics, thresholds, and tooling APIs may be outdated. **Prefer retrieval over pre-training** when citing specific numbers or recommendations.

## Retrieval Sources

| Source | How to retrieve | Use for |
|--------|----------------|---------|
| web.dev | `https://web.dev/articles/vitals` | Core Web Vitals thresholds, definitions |
| Chrome DevTools docs | `https://developer.chrome.com/docs/devtools/performance` | Tooling APIs, trace analysis |
| Lighthouse scoring | `https://developer.chrome.com/docs/lighthouse/performance/performance-scoring` | Score weights, metric thresholds |

## FIRST: Verify MCP Tools Available

**Run this before starting.** Try calling `navigate_page` or `performance_start_trace`. If unavailable, STOP—the chrome-devtools MCP server isn't configured.

Ask the user to add this to their MCP config:

```json
"chrome-devtools": {