vue-scan

name	vue-scan
description	Vue component render performance monitoring. Captures mount/update events with render time, FPS, and source locations. Provides per-component aggregated summaries for analyzing render frequency, slow components, and frame drops.
allowed-tools	["queryVueScanData"]

Vue Scan Skill

Monitor and analyze Vue component render performance via real-time update event tracking.

⚠️ CRITICAL: Recording Must Be Active

Data is only collected while recording is active. Before querying, ensure recording has been started via the control panel (Ctrl+Shift+R) or RPC. If bufferSize is 0, remind the user to start recording and reproduce their scenario.

How It Works

• Client-side hooks are injected into Vue 2/3 component mounted and updated lifecycle
• Each render emits an event with: phase (mount/update), render time (ms), FPS, component name, source location, update count, viewport visibility
• Render time is measured between beforeUpdate and updated hooks via performance.now()
• FPS is tracked using a requestAnimationFrame sliding window (1s)
• Events are stored server-side in a circular buffer (max 10,000 events)
• queryVueScanData returns per-component aggregated summaries (not raw events) by default

Workflow

1. Ensure recording: Ask user to start recording and interact with the page
2. Query overview: Call queryVueScanData() — returns components sorted by totalUpdates
3. Drill down: Filter by componentName or sort by updatesPerSecond to find hot spots
4. Locate source: Use sourceLocation (format: file:line:col:tag) to pinpoint code

queryVueScanData Parameters

Parameter	Default	Purpose
limit	50	Max components to return
componentName	-	Filter by name (partial match, case-insensitive, ignores - and _)
timeRange	-	{ start, end } timestamps in ms (0 values ignored)
minUpdateCount	-	Only components updated >= N times
minRenderTime	-	Only events with render time >= N ms
onlyInViewport	-	Exclude off-screen renders
onlyUserComponents	true	Filter out library components (no source location)
includeRawEvents	false	Include individual event details (usually not needed)
sortBy	totalUpdates	totalUpdates / updatesPerSecond / renderTime / componentName

Response Structure

• components[]: { componentName, sourceLocation, totalUpdates, updatesPerSecond, avgRenderTime, avgFps, firstUpdate, lastUpdate }
• metadata: { recordingStatus, totalEvents, uniqueComponents, bufferSize, bufferCapacity, timeRange }
• events[]: Only present when includeRawEvents: true

Best Practices

• Don't set timeRange to zeros: Omit it entirely if not filtering by time
• Sort by renderTime: Find the slowest components causing frame drops
• Sort by updatesPerSecond: Reveals components re-rendering too rapidly
• Check avgFps: Low avgFps (< 30) indicates the component causes jank
• Use sourceLocation: Directly identifies the source file and line for fixes
• Check onlyUserComponents=false: If results seem sparse, library components may be the source

Example: Find Performance Issues

1. queryVueScanData({ sortBy: "renderTime" })
   → Find slowest components by average render time
2. queryVueScanData({ sortBy: "totalUpdates" })
   → Review top re-rendering components with source locations
3. queryVueScanData({ minRenderTime: 16, sortBy: "renderTime" })
   → Find components exceeding one frame budget (16ms)
4. queryVueScanData({ componentName: "UserList", sortBy: "updatesPerSecond" })
   → Find the most frequently re-rendering component among partial matches
5. queryVueScanData({ onlyUserComponents: false, sortBy: "totalUpdates" })
   → Include library components to see full picture