Web Perf
CloudflareOfficialPublished by Cloudflare
- Skill
- Review and audit
- Cloud and DevOps
- Apache-2.0
- No issues found
From the skill’s files
Taken from the skill’s own files (its description, section headings and stated usage). Not an AutoGineer summary, and not written by the author as one.
Audit, diagnose, or optimize website loading and interaction performance, Core Web Vitals, and Lighthouse performance scores. Your knowledge of web performance metrics, thresholds, and tooling APIs may be outdated. Prefer retrieval over pre-training when citing specific numbers or recommendations.
What it does
- Retrieval Sources
- FIRST: Verify MCP Tools Available
- Key Guidelines
- Quick Reference
- Workflow
- Phase 5: Codebase Analysis
When to use it
The skill’s files do not state this.
Advantages
The skill’s files do not state this.
Usage examples
The skill’s files do not state this.
Install
Download the skill as a ZIP:
https://autogineer.com/agent-skills/cloudflare/web-perf/downloadUnzip it into the cross-client skills folder of your project:
mkdir -p .agents/skills && unzip web-perf.zip -d .agents/skills
Documentation by Cloudflare
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Your knowledge of web performance metrics, thresholds, and tooling APIs may be outdated.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
Discover available browser and performance tools before starting. Use the capabilities available for the requested audit. If trace tools are unavailable, continue any useful source or network analysis and state which measurements could not be collected.
If the user wants Chrome DevTools MCP setup, consult its installation guide and use the latest package version. Only change MCP configuration when setup is within the user's authorized scope; otherwise ask first. For clients using command and args, an example server entry is:
"chrome-devtools": {
"command": "npx",
"args": ["-y", "chrome-devtools-mcp@latest"]
}Key Guidelines
Be assertive: Verify claims by checking network requests, DOM, or codebase—then state findings definitively.
Verify before recommending: Confirm something is unused before suggesting removal.
Quantify impact: Use estimated savings from insights. Don't prioritize changes with 0ms impact.
Skip non-issues: If render-blocking resources have 0ms estimated impact, note but don't recommend action.
Be specific: Say "compress hero.png (450KB) to WebP" not "optimize images".
Prioritize ruthlessly: A site with 200ms LCP and 0 CLS is already excellent—say so.
Quick Reference
| 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) |
Workflow
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)Phase 1: Performance Trace
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:
If trace returns empty or fails, verify the page loaded correctly with
navigate_pagefirstIf insight names don't match, inspect the trace response to list available insights
Phase 2: Core Web Vitals Analysis
Use 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):
TTFB: < 800ms / < 1.8s / > 1.8s
FCP: < 1.8s / < 3s / > 3s
LCP: < 2.5s / < 4s / > 4s
INP: < 200ms / < 500ms / > 500ms
TBT: < 200ms / < 600ms / > 600ms
CLS: < 0.1 / < 0.25 / > 0.25
Speed Index: < 3.4s / < 5.8s / > 5.8s
Phase 3: Network Analysis
List all network requests to identify optimization opportunities:
list_network_requests(resourceTypes: ["Script", "Stylesheet", "Document", "Font", "Image"])Look for:
Render-blocking resources: JS/CSS in
<head>withoutasync/defer/mediaattributesNetwork chains: Resources discovered late because they depend on other resources loading first (e.g., CSS imports, JS-loaded fonts)
Missing preloads: Critical resources (fonts, hero images, key scripts) not preloaded
Caching issues: Missing or weak
Cache-Control,ETag, orLast-ModifiedheadersLarge payloads: Uncompressed or oversized JS/CSS bundles
Unused preconnects: If flagged, verify by checking if ANY requests went to that origin. If zero requests, it's definitively unused—recommend removal. If requests exist but loaded late, the preconnect may still be valuable.
For detailed request info:
get_network_request(reqid: <id>)Phase 4: Accessibility Snapshot
Take an accessibility tree snapshot:
take_snapshot(verbose: true)Flag high-level gaps:
Missing or duplicate ARIA IDs
Elements with poor contrast ratios (check against WCAG AA: 4.5:1 for normal text, 3:1 for large text)
Focus traps or missing focus indicators
Interactive elements without accessible names
Phase 5: Codebase Analysis
Skip if auditing a third-party site without codebase access.
Analyze the codebase to understand where improvements can be made.
Detect Framework & Bundler
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.
Tree-Shaking & Dead Code
Webpack: Check for
mode: 'production',sideEffectsin package.json,usedExportsoptimizationVite/Rollup: Tree-shaking enabled by default; check for
treeshakeoptionsLook for: Barrel files (
index.jsre-exports), large utility libraries imported wholesale (lodash, moment)
Unused JS/CSS
Check for CSS-in-JS vs. static CSS extraction
Look for PurgeCSS/UnCSS configuration (Tailwind's
contentconfig)Identify dynamic imports vs. eager loading
Polyfills
Check for
@babel/preset-envtargets anduseBuiltInssettingLook for
core-jsimports (often oversized)Check
browserslistconfig for overly broad targeting
Compression & Minification
Check for
terser,esbuild, orswcminificationLook for gzip/brotli compression in build output or server config
Check for source maps in production builds (should be external or disabled)
Output Format
Present findings as:
Core Web Vitals Summary - Table with metric, value, and rating (good/needs-improvement/poor)
Top Issues - Prioritized list of problems with estimated impact (high/medium/low)
Recommendations - Specific, actionable fixes with code snippets or config changes
Codebase Findings - Framework/bundler detected, optimization opportunities (omit if no codebase access)
Skill feedback
If the user reports that this skill gave incorrect or outdated guidance, or is missing information, read references/skill-feedback.md.
Files
- ATTRIBUTION.mdAdded by AutoGineer852 B
- LICENSELicence file added by AutoGineer11.1 KiB
- SKILL.md8.2 KiB
- references/skill-feedback.md2.7 KiB
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Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta
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Attribution and licence
- Published by
- Cloudflare
- Publisher
- Cloudflare (Official)
- Source
- cloudflare/skills · skills/web-perf · commit 6eb6c78
- Licence
- Apache License 2.0 (redistribution allowed)
- LICENSE (added by AutoGineer from LICENSE)
- ATTRIBUTION.md (written by AutoGineer)
- Synced
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