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webperf-resources

Testing & Quality
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Intelligent network quality analysis with adaptive loading strategies. Detects connection type (2g/3g/4g), bandwidth, RTT, and save-data mode, then automatically triggers appropriate optimization workflows. Includes decision trees that recommend image compression for slow connections, critical CSS inlining for high RTT, and save-data optimizations (disable autoplay, reduce quality). Features connection-aware performance budgets (500KB for 2g, 1.5MB for 3g, 3MB for 4g+) and adaptive loading implementation guides. Cross-skill integration with Loading (TTFB impact), Media (responsive images), and Core Web Vitals (connection impact on LCP/INP). Use when the user asks about slow connections, mobile optimization, save-data support, or adaptive loading strategies. Compatible with Chrome DevTools MCP.

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How to use this skill

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Source SKILL.md: https://github.com/nucliweb/webperf-snippets/blob/HEAD/.claude/skills/webperf-resources/SKILL.md

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WebPerf: Resources & Network

JavaScript snippets for measuring web performance in Chrome DevTools. Execute with mcp__chrome-devtools__evaluate_script, capture output with mcp__chrome-devtools__get_console_message.

Scripts

  • scripts/Network-Bandwidth-Connection-Quality.js — Network Bandwidth & Connection Quality

Common Workflows

Network Quality Assessment

When the user asks about network performance, connection quality, or adaptive loading:

  1. Network-Bandwidth-Connection-Quality.js - Analyze network bandwidth, effective connection type, RTT, downlink, save-data mode

Adaptive Loading Strategy

When implementing adaptive loading or the user asks "how to optimize for slow connections":

  1. Network-Bandwidth-Connection-Quality.js - Detect connection quality
  2. Cross-reference with webperf-loading skill:
    • TTFB.js (measure server response on slow connections)
    • Find-render-blocking-resources.js (identify heavy resources to defer)
    • Resource-Hints-Validation.js (optimize preconnect for slow networks)
  3. Cross-reference with webperf-media skill:
    • Image-Element-Audit.js (implement responsive images based on connection)
    • Video-Element-Audit.js (adjust video quality based on connection)

Save-Data Mode Detection

When the user asks about save-data or data-saving features:

  1. Network-Bandwidth-Connection-Quality.js - Check if save-data is enabled
  2. If save-data is enabled, recommend:
    • Reducing image quality
    • Disabling autoplay videos
    • Deferring non-critical resources
    • Using low-res thumbnails

Mobile/Slow Connection Optimization

When the user asks "optimize for mobile" or "slow connection users":

  1. Network-Bandwidth-Connection-Quality.js - Assess connection type
  2. Cross-reference with webperf-loading skill:
    • TTFB.js (critical for slow connections)
    • Find-render-blocking-resources.js (minimize blocking on slow networks)
    • Critical-CSS-Detection.js (inline critical CSS to reduce RTT)
    • Prefetch-Resource-Validation.js (avoid excessive prefetch on slow connections)

Decision Tree

Use this decision tree to automatically run follow-up snippets based on results:

After Network-Bandwidth-Connection-Quality.js

  • If effectiveType is "slow-2g" or "2g" → Very slow connection, recommend:

    1. Run webperf-loading:Critical-CSS-Detection.js (inline critical CSS)
    2. Run webperf-media:Image-Element-Audit.js (implement aggressive lazy loading)
    3. Run webperf-loading:Prefetch-Resource-Validation.js (remove prefetch to save bandwidth)
    4. Run webperf-core-web-vitals:LCP.js (LCP is heavily impacted by slow connections)
    5. Recommend minimal resource strategy

  • If effectiveType is "3g" → Moderate connection, recommend:

    1. Run webperf-loading:Find-render-blocking-resources.js (minimize blocking)
    2. Run webperf-media:Image-Element-Audit.js (responsive images)
    3. Run webperf-loading:Resource-Hints-Validation.js (optimize preconnect)
    4. Run webperf-core-web-vitals:INP.js (high latency can impact interaction responsiveness)
    5. Implement adaptive image quality

  • If effectiveType is "4g" or better → Good connection, recommend:

    1. Standard optimization practices
    2. Consider strategic prefetch for navigation
    3. Higher quality media is acceptable

  • If save-data is enabled → User explicitly wants to save data, recommend:

    1. Reduce image quality aggressively
    2. Disable autoplay videos
    3. Defer non-critical resources
    4. Remove prefetch/preload hints
    5. Show "high quality" toggle option

  • If RTT > 300ms → High latency, recommend:

    1. Run webperf-loading:TTFB.js (latency impacts TTFB)
    2. Run webperf-loading:TTFB-Sub-Parts.js (break down latency components)
    3. Run webperf-loading:Resource-Hints-Validation.js (preconnect critical for high RTT)
    4. Run webperf-loading:Service-Worker-Analysis.js (caching is critical for high latency)
    5. Minimize number of origins
    6. Use HTTP/2 or HTTP/3 for multiplexing

  • If downlink < 1 Mbps → Very limited bandwidth, recommend:

    1. Run webperf-media:Image-Element-Audit.js (aggressive compression)
    2. Run webperf-media:Video-Element-Audit.js (disable autoplay)
    3. Run webperf-loading:Prefetch-Resource-Validation.js (remove prefetch)
    4. Implement bandwidth-aware loading

  • If downlink > 10 Mbps → Good bandwidth, consider:

    • Higher quality media
    • Strategic prefetch
    • Preloading next-page resources

Adaptive Loading Implementation Guide

Based on Network Information API results, implement these strategies:

For slow-2g / 2g (< 50 Kbps): (effectiveType: "slow-2g" or "2g")

  • Serve low-res images (quality: 30-40)
  • Disable autoplay videos
  • Remove all prefetch hints
  • Inline all critical CSS
  • Defer all non-critical JavaScript
  • Use system fonts (no webfonts)
  • Aggressive lazy loading (load on scroll + buffer)

For 3g (50-700 Kbps): (effectiveType: "3g")

  • Serve medium-res images (quality: 60-70)
  • Disable autoplay videos
  • Limited prefetch (critical only)
  • Inline critical CSS only
  • Defer non-critical JavaScript
  • Preload 1-2 critical fonts
  • Standard lazy loading

For 4g+ (> 700 Kbps): (effectiveType: "4g")

  • Serve high-res images (quality: 80-90)
  • Allow autoplay videos (muted)
  • Strategic prefetch for navigation
  • Standard CSS loading and JavaScript loading
  • Preload critical fonts
  • Standard lazy loading

For save-data mode: (navigator.connection.saveData === true)

  • Override connection type, treat as worse than actual
  • Show "Load high quality" toggle
  • Disable autoplay entirely
  • Minimal images, minimal quality
  • No prefetch, no preload (except critical)

Performance Budget by Connection Type

Adjust performance budgets based on connection quality:

slow-2g / 2g:

  • Total page weight: < 500KB
  • Images: < 200KB total
  • JavaScript: < 100KB total
  • No videos

3g:

  • Total page weight: < 1.5MB
  • Images: < 800KB total
  • JavaScript: < 300KB total
  • Videos: < 3MB (only if critical)

4g+:

  • Total page weight: < 3MB
  • Images: < 2MB total
  • JavaScript: < 1MB total
  • Videos: < 10MB

Network Information API Limitations

Be aware of API limitations and fallbacks:

API not available:

  • Safari does not support Network Information API
  • Fallback: Use TTFB as proxy for connection quality
  • Fallback: Device detection (mobile = assume slow)
  • Fallback: User preference toggle

API values are estimates:

  • effectiveType is based on recent observations
  • Values can change during session
  • Re-check periodically for long sessions

Privacy considerations:

  • Some browsers limit precision for privacy
  • Values may be rounded or capped
  • Consider user privacy when making decisions

References

  • references/snippets.md — Descriptions and thresholds for each script
  • references/schema.md — Return value schema for interpreting script output