# profiling-performance

This skill profiles web application CPU performance using browser MCP tools. It captures call stacks and pinpoints slow functions causing interface lag.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 410 installs · ★ 866
- Author: spencerpauly
- License: CC0-1.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/spencerpauly/awesome-cursor-skills/tree/HEAD/resources/profiling-performance/SKILL.md
- Updated: 2026-08-02
- HTML: https://affpapa.org/en/nevibecode/skills/profiling-performance

## What it does

The skill automates web application CPU profiling through the `cursor-ide-browser` MCP server. The agent opens a target local page, invokes `browser_profile_start`, simulates clicks or scrolling, and captures performance traces with `browser_profile_stop`.

Captured profiles are written to `~/.cursor/browser-logs/` as raw Chrome DevTools JSON files and Markdown summaries. By inspecting `hitCount` and function names in call frames, the agent detects main-thread blocking, unnecessary re-renders, and heavy external library calls.

A running local server is required before profiling begins. Profiling in React development mode introduces extra runtime overhead, so measuring a production build provides much more reliable numbers. The summary file can miss subtle execution details, which makes reading raw JSON mandatory.

## Requirements
- Works with: Chrome

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add spencerpauly/awesome-cursor-skills --skill profiling-performance -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/profiling-performance/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/profiling-performance/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add spencerpauly/awesome-cursor-skills --skill profiling-performance -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/profiling-performance/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add spencerpauly/awesome-cursor-skills --skill profiling-performance -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/profiling-performance/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install spencerpauly/awesome-cursor-skills profiling-performance
```

2. **Manually: put the files in place**
- File: `.github/skills/profiling-performance/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add spencerpauly/awesome-cursor-skills --skill profiling-performance -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/spencerpauly/awesome-cursor-skills --path resources/profiling-performance
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/profiling-performance/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add spencerpauly/awesome-cursor-skills --skill profiling-performance -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/spencerpauly/awesome-cursor-skills/tree/HEAD/resources/profiling-performance/SKILL.md

## When to use it
- capture CPU profiles during page interactions
- locate synchronous functions blocking the browser main thread
- identify redundant React component re-renders
- compare execution samples before and after code changes

## Example prompts
- Profile CPU performance on the orders page and find out why scrolling lags.
- Record a profile while submitting the search form and pinpoint slow functions.
- Inspect the raw profile JSON in browser-logs and suggest ways to reduce re-renders.

## Source text · SKILL.md · CC0-1.0

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````text
---
name: profiling-performance
description: Profile a running web application's CPU performance using Cursor's built-in browser profiler. Captures call stacks, identifies slow functions, and suggests optimizations. Use when a page feels slow or janky.
---

# Performance Profile

Use this skill when a web application feels slow, janky, or unresponsive. Cursor's built-in browser has CPU profiling tools that capture real call stacks and timing data.

## How It Works

The `cursor-ide-browser` MCP provides `browser_profile_start` and `browser_profile_stop` tools that capture Chrome DevTools-format CPU profiles. Profile data is written to `~/.cursor/browser-logs/` as both raw JSON and a human-readable summary.

## Steps

1. **Ensure the app is running** — start the dev server if it isn't already running.

2. **Navigate to the slow page**:

   ```
   Tool: browser_navigate
   Arguments: { "url": "http://localhost:3000/slow-page" }
   ```

3. **Start profiling**:

   ```
   Tool: browser_profile_start
   ```

4. **Reproduce the slow interaction** — use browser tools to trigger the slow behavior:
   - Click buttons, scroll, type in inputs, navigate between pages
   - Use `browser_click`, `browser_scroll`, `browser_fill` to interact
   - Wait a few seconds for the interaction to complete

5. **Stop profiling**:

   ```
   Tool: browser_profile_stop
   ```

   This writes two files to `~/.cursor/browser-logs/`:
   - `cpu-profile-{timestamp}.json` — raw Chrome DevTools profile
   - `cpu-profile-{timestamp}-summary.md` — human-readable summary

6. **Analyze the results** — read both files. Key things to look for in the raw JSON:
   - `profile.nodes[].hitCount` — how many samples hit each function
   - `profile.nodes[].callFrame.functionName` — the function names
   - `profile.samples.length` — total number of samples collected

   Cross-reference with the summary to identify:
   - Functions consuming the most CPU time
   - Unexpected re-renders or layout thrashing
   - Expensive third-party library calls
   - Synchronous operations blocking the main thread

7. **Suggest fixes** — based on the profile data, recommend specific optimizations:
   - Memoize expensive computations
   - Debounce rapid event handlers
   - Move heavy work to a Web Worker
   - Lazy-load components or routes
   - Virtualize long lists

## Notes

- Always read the raw `.json` profile to verify the summary — the summary can miss nuances.
- Profile in development mode first, but be aware that React dev mode adds overhead. For accurate measurements, profile a production build.
````
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First 2599 of 2763 bytes. © spencerpauly · CC0-1.0 · https://github.com/spencerpauly/awesome-cursor-skills/tree/HEAD/resources/profiling-performance/SKILL.md

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