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Analyzes web performance using Chrome DevTools MCP. Measures Core Web Vitals (FCP, LCP, TBT, CLS, 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.
npx claudepluginhub ruslands/plugins --plugin web-performance-skillsHow this skill is triggered — by the user, by Claude, or both
Slash command
/web-performance-skills:web-performance-optimizationThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
Your knowledge of web performance metrics, thresholds, and tooling APIs may be outdated. **Prefer retrieval over pre-training** when citing specific numbers or recommendations.
Guides Next.js Cache Components and Partial Prerendering (PPR): 'use cache' directives, cacheLife(), cacheTag(), revalidateTag() for caching, invalidation, static/dynamic optimization. Auto-activates on cacheComponents: true.
Migrates code, prompts, and API calls from Claude Sonnet 4.0/4.5 or Opus 4.1 to Opus 4.5, updating model strings on Anthropic, AWS, GCP, Azure platforms.
Breaks plans, specs, or PRDs into thin vertical-slice issues on the project issue tracker using tracer bullets. Useful for converting high-level work into grabbable implementation tickets.
Share bugs, ideas, or general feedback.
Your knowledge of web performance metrics, thresholds, and tooling APIs may be outdated. Prefer retrieval over pre-training when citing specific numbers or recommendations.
| 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 |
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:
"chrome-devtools": {
"type": "local",
"command": ["npx", "-y", "chrome-devtools-mcp@latest"]
}
| Task | Tool Call |
|---|---|
| Load page | navigate_page(url: "...") |
| Start trace | performance_start_trace(autoStop: true, reload: true) |
| Analyze insight | performance_analyze_insight(insightSetId: "...", insightName: "...") |
| List requests | list_network_requests(resourceTypes: ["Script", "Stylesheet", ...]) |
| Request details | get_network_request(reqid: <id>) |
| A11y snapshot | take_snapshot(verbose: true) |
Copy this checklist to track progress:
Audit Progress:
- [ ] Phase 1: Performance trace (navigate + record)
- [ ] Phase 2: Core Web Vitals analysis (includes CLS culprits)
- [ ] Phase 3: Network analysis
- [ ] Phase 4: Accessibility snapshot
- [ ] Phase 5: Codebase analysis (skip if third-party site)
Navigate to the target URL:
navigate_page(url: "<target-url>")
Start a performance trace with reload to capture cold-load metrics:
performance_start_trace(autoStop: true, reload: true)
Wait for trace completion, then retrieve results.
Troubleshooting:
navigate_page firstUse performance_analyze_insight to extract key metrics.
Note: Insight names may vary across Chrome DevTools versions. If an insight name doesn't work, check the insightSetId from the trace response to discover available insights.
Common insight names:
| Metric | Insight Name | What to Look For |
|---|---|---|
| LCP | LCPBreakdown | Time to largest contentful paint; breakdown of TTFB, resource load, render delay |
| CLS | CLSCulprits | Elements causing layout shifts (images without dimensions, injected content, font swaps) |
| Render Blocking | RenderBlocking | CSS/JS blocking first paint |
| Document Latency | DocumentLatency | Server response time issues |
| Network Dependencies | NetworkRequestsDepGraph | Request chains delaying critical resources |
Example:
performance_analyze_insight(insightSetId: "<id-from-trace>", insightName: "LCPBreakdown")
Key thresholds (good/needs-improvement/poor):
List all network requests to identify optimization opportunities:
list_network_requests(resourceTypes: ["Script", "Stylesheet", "Document", "Font", "Image"])
Look for:
<head> without async/defer/media attributesCache-Control, ETag, or Last-Modified headersFor detailed request info:
get_network_request(reqid: <id>)
Take an accessibility tree snapshot:
take_snapshot(verbose: true)
Flag high-level gaps:
Skip if auditing a third-party site without codebase access.
Analyze the codebase to understand where improvements can be made.
Search for configuration files to identify the stack:
| Tool | Config Files |
|---|---|
| Webpack | webpack.config.js, webpack.*.js |
| Vite | vite.config.js, vite.config.ts |
| Rollup | rollup.config.js, rollup.config.mjs |
| esbuild | esbuild.config.js, build scripts with esbuild |
| Parcel | .parcelrc, package.json (parcel field) |
| Next.js | next.config.js, next.config.mjs |
| Nuxt | nuxt.config.js, nuxt.config.ts |
| SvelteKit | svelte.config.js |
| Astro | astro.config.mjs |
Also check package.json for framework dependencies and build scripts.
mode: 'production', sideEffects in package.json, usedExports optimizationtreeshake optionsindex.js re-exports), large utility libraries imported wholesale (lodash, moment)content config)@babel/preset-env targets and useBuiltIns settingcore-js imports (often oversized)browserslist config for overly broad targetingterser, esbuild, or swc minificationPresent findings as: