webperf-interaction

What this skill does

# WebPerf: Interaction & Animation

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/Forced-Synchronous-Layout.js` — Forced Synchronous Layout Detector
- `scripts/Input-Latency-Breakdown.js` — Input Latency Breakdown
- `scripts/Interactions.js` — Interactions
- `scripts/Layout-Shift-Loading-and-Interaction.js` — Layout Shift Tracking
- `scripts/Long-Animation-Frames-Helpers.js` — LoAF Helpers
- `scripts/Long-Animation-Frames-Script-Attribution.js` — Long Animation Frames Script Attribution
- `scripts/Long-Animation-Frames.js` — Long Animation Frames (LoAF)
- `scripts/LongTask.js` — Long Tasks
- `scripts/Scroll-Performance.js` — Scroll Performance Analysis


## Common Workflows

### Complete Interaction Performance Audit

When the user asks for interaction analysis or "audit responsiveness":

1. **Interactions.js** - List all user interactions with timing
2. **Input-Latency-Breakdown.js** - Break down interaction phases
3. **Long-Animation-Frames.js** - Detect blocking animation frames
4. **LongTask.js** - Identify long tasks blocking the main thread
5. **Scroll-Performance.js** - Measure scroll smoothness

### INP Deep Dive

When INP is slow (>200ms) or the user asks "debug INP" or "slow interactions":

1. **Interactions.js** - Identify which interactions are slow
2. **Input-Latency-Breakdown.js** - Break down into input delay, processing time, presentation delay
3. **Long-Animation-Frames.js** - Find animation frames >50ms that block interactions
4. **Long-Animation-Frames-Script-Attribution.js** - Identify scripts causing the blocking
5. **Long-Animation-Frames-Helpers.js** - Get detailed timing and attribution helpers

### Scroll Jank Investigation

When the user reports "scroll jank", "choppy scrolling", or "scroll performance issues":

1. **Scroll-Performance.js** - Measure scroll smoothness and frame drops
2. **Long-Animation-Frames.js** - Detect frames causing jank (>50ms)
3. **Layout-Shift-Loading-and-Interaction.js** - Check for layout shifts during scroll
4. **Long-Animation-Frames-Script-Attribution.js** - Find scripts running during scroll

### Main Thread Blocking Analysis

When the page feels unresponsive or the user asks "why is the page frozen":

1. **LongTask.js** - List all tasks >50ms blocking the main thread
2. **Long-Animation-Frames.js** - Correlate with animation frame timing
3. **Long-Animation-Frames-Script-Attribution.js** - Attribute blocking to specific scripts
4. Cross-reference with **webperf-loading** skill:
   - JS-Execution-Time-Breakdown.js (script parsing/execution time)
   - First-And-Third-Party-Script-Info.js (identify third-party blockers)

### Layout Shift During Interaction

When the user reports "things move when I click" or CLS issues during interaction:

1. **Layout-Shift-Loading-and-Interaction.js** - Separate loading vs interaction shifts
2. **Interactions.js** - Correlate shifts with specific interactions
3. **CLS.js** (from Core Web Vitals skill) - Measure total CLS
4. Cross-reference with **webperf-media** skill:
   - Image-Element-Audit.js (images without dimensions causing shifts)

### Animation Performance Analysis

When animations feel sluggish or the user asks "debug animation performance":

1. **Long-Animation-Frames.js** - Identify frames taking too long to render
2. **Long-Animation-Frames-Helpers.js** - Detailed frame timing analysis
3. **Long-Animation-Frames-Script-Attribution.js** - Find scripts delaying frames
4. **Scroll-Performance.js** - If scroll animations are involved

### Third-Party Script Impact on Interactions

When interactions are slow and third-party scripts are suspected:

1. **Long-Animation-Frames-Script-Attribution.js** - Identify third-party scripts in long frames
2. **LongTask.js** - Measure long task frequency
3. Cross-reference with **webperf-loading** skill:
   - First-And-Third-Party-Script-Info.js (list all third-party scripts)
   - First-And-Third-Party-Script-Timings.js (measure script loading impact)
   - Script-Loading.js (check for blocking scripts)

## Decision Tree

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

### After Interactions.js

- **If any interaction > 200ms** → Run **Input-Latency-Breakdown.js** on slow interactions; also run **webperf-core-web-vitals:INP.js** for official INP measurement
- **If many interactions > 200ms** → Main thread congestion, run:
  1. **Long-Animation-Frames.js** (blocking frames)
  2. **LongTask.js** (long tasks)
  3. **Long-Animation-Frames-Script-Attribution.js** (culprit scripts)
- **If specific interaction types are slow (e.g., click vs keyboard)** → Focus on that interaction type
- **If interactions occur during page load** → Cross-check with **webperf-loading:JS-Execution-Time-Breakdown.js**

### After Input-Latency-Breakdown.js

- **If Input Delay > 50ms** → Main thread was busy, run:
  1. **Long-Animation-Frames.js** (what was blocking)
  2. **LongTask.js** (long task before interaction)
- **If Processing Time > 100ms** → Heavy event handlers, run:
  1. **Long-Animation-Frames-Script-Attribution.js** (which scripts)
  2. **webperf-loading:First-And-Third-Party-Script-Info.js** (third-party involvement)
- **If Presentation Delay > 50ms** → Rendering bottleneck, run:
  1. **Long-Animation-Frames.js** (frame rendering time)
  2. **Layout-Shift-Loading-and-Interaction.js** (check for layout work)

### After Long-Animation-Frames.js

- **If many frames > 50ms** → Run **Long-Animation-Frames-Script-Attribution.js** to identify causes
- **If frames > 100ms** → Critical blocking, run:
  1. **Long-Animation-Frames-Script-Attribution.js** (detailed attribution)
  2. **LongTask.js** (related long tasks)
  3. **webperf-loading:JS-Execution-Time-Breakdown.js** (script execution cost)
- **If frames occur during scroll** → Run **Scroll-Performance.js** to measure impact
- **If frames occur during page load** → Cross-check with **webperf-loading:Event-Processing-Time.js**

### After Long-Animation-Frames-Script-Attribution.js

- **If third-party scripts are causing long frames** → Run:
  1. **webperf-loading:First-And-Third-Party-Script-Info.js** (list all third-party scripts)
  2. **webperf-loading:Script-Loading.js** (check loading strategy)
  3. Recommend deferring or removing problematic scripts
- **If first-party scripts are causing long frames** → Recommend:
  - Code splitting
  - Debouncing/throttling event handlers
  - Web Workers for heavy computation
- **If forced reflow/layout detected** → Analyze DOM manipulation patterns

### After LongTask.js

- **If many long tasks (>5)** → Main thread is congested, run:
  1. **Long-Animation-Frames-Script-Attribution.js** (detailed attribution)
  2. **webperf-loading:JS-Execution-Time-Breakdown.js** (script execution analysis)
  3. **webperf-loading:First-And-Third-Party-Script-Info.js** (identify heavy scripts)
- **If long tasks > 500ms** → Critical blocking, investigate:
  - Synchronous third-party scripts
  - Heavy computation without Web Workers
  - Excessive DOM manipulation
- **If long tasks correlate with interactions** → Run **Interactions.js** to see impact

### After Scroll-Performance.js

- **If scroll FPS < 30** → Severe jank, run:
  1. **Long-Animation-Frames.js** (blocking frames during scroll)
  2. **Long-Animation-Frames-Script-Attribution.js** (scripts running on scroll)
  3. **Layout-Shift-Loading-and-Interaction.js** (layout work during scroll)
- **If scroll FPS 30-50** → Noticeable jank, investigate:
  - Scroll event handlers
  - Passive event listeners
  - CSS will-change properties
- **If scroll FPS > 50** → Good, but check for layout shifts during scroll

### After Layout-Shift-Loading-and-Interaction.js

- **If shifts occur during page load** → Cross-reference with **webperf-core-web-vitals:CLS.js**
- **If shifts occur during interaction** → This impacts INP a