# performance-profiling

Guides performance profiling for Apple apps using Instruments and MetricKit. It directs the AI agent to pinpoint hangs and slow launch times.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1400 installs · ★ 7001
- Author: MengTo
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/MengTo/Skills/tree/HEAD/agent-skills/codex/performance-profiling/SKILL.md
- Updated: 2026-10-25
- HTML: https://affpapa.org/en/nevibecode/skills/mengto-performance-profiling

## What it does

This skill equips coding agents with a structured approach to Apple app diagnostics. Instead of guessing, it routes the workflow through a decision tree based on concrete symptoms. It points to dedicated guides for Time Profiler, Allocations, and launch optimization. UI hangs exceeding 250 milliseconds and memory leaks get targeted investigation steps.

The workflow enforces strict diagnostic hygiene. Simulator profiling skews data because it runs on the host machine CPU and memory. You must test on a physical device using a Release build where compiler optimizations reflect production reality.

For production metrics, the skill supplies ready-to-use Swift snippets for MetricKit subscribers to capture launch latency and hang payloads. It also provides pre-release checks covering `@MainActor` isolation and `os_signpost` instrumentation.

## Install

### Claude Code (native platform)

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

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

### Codex

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

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

### Cursor

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

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install MengTo/Skills performance-profiling
```

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

### Gemini CLI

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

2. **Platform CLI**
```bash
gemini skills install https://github.com/MengTo/Skills --path agent-skills/codex/performance-profiling
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add MengTo/Skills --skill performance-profiling -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/MengTo/Skills/tree/HEAD/agent-skills/codex/performance-profiling/SKILL.md

## When to use it
- isolate main thread hangs exceeding 250 ms
- track down memory leaks and retain cycles in closures
- reduce cold launch time and time to first frame
- implement MetricKit subscribers for production telemetry

## Example prompts
- Analyze this main thread hang report and suggest fixes based on Time Profiler data
- Add a MetricKit subscriber to track launch metrics and hang diagnostics in production
- Audit this SwiftUI view model against the memory and responsiveness checklist

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 40fe59c6634a4c31.

BEGIN THIRD-PARTY FILE 40fe59c6634a4c31
````text
---
name: performance-profiling
description: Guide performance profiling for Apple platform apps with Instruments, Xcode diagnostics, and MetricKit. Use when investigating app hangs, stutters, high CPU, memory leaks, memory growth, OOM crashes, slow launch, battery drain, thermal issues, App Store performance readiness, or when adding os_signpost and measurement hooks.
---

# Performance Profiling

Use this skill to diagnose Apple app performance issues systematically, pick the right profiling workflow, apply targeted fixes, and verify the change with real measurements.

## Decision Tree

Choose the reference file before changing code:

```text
What performance problem are you investigating?

+ App hangs, stutters, dropped frames, slow UI, high CPU
  -> Read references/time-profiler.md

+ High memory, leaks, OOM crashes, growing footprint
  -> Read references/memory-profiling.md

+ Slow cold launch, warm launch, resume, or time to first frame
  -> Read references/launch-optimization.md

+ Battery drain, thermal throttling, background energy, network waste
  -> Read references/energy-diagnostics.md

+ General "app feels slow"
  -> Start with references/time-profiler.md, then references/memory-profiling.md

+ Pre-release performance audit
  -> Read all reference files and use the review checklist below
```

## Quick Reference

| Problem | Instrument / Tool | Key Metric | Reference |
| --- | --- | --- | --- |
| UI hangs over 250 ms | Time Profiler + Hangs | Hang duration, main thread stack | `references/time-profiler.md` |
| High CPU usage | Time Profiler | CPU percent by function, call tree weight | `references/time-profiler.md` |
| Memory leak | Leaks + Memory Graph | Leaked bytes, retain cycle paths | `references/memory-profiling.md` |
| Memory growth | Allocations | Live bytes, generation analysis | `references/memory-profiling.md` |
| Slow launch | App Launch | Time to first frame, pre-main, post-main | `references/launch-optimization.md` |
| Battery drain | Energy Log | Energy impact, CPU/GPU/network activity | `references/energy-diagnostics.md` |
| Thermal issues | Activity Monitor, Instruments | Thermal state transitions | `references/energy-diagnostics.md` |
| Network waste | Network profiler | Redundant fetches, payload size | `references/energy-diagnostics.md` |

## Workflow

1. Identify the performance category from the user report, traces, logs, or code path.
2. Read only the matching reference file unless the issue is broad or unclear.
3. Prefer real device profiling with a Release build and representative data.
4. Inspect the code path named by the profile before proposing a fix.
5. Apply the smallest targeted fix that addresses the measured bottleneck.
6. Re-profile or add a repeatable measurement to confirm the improvement.

## Profiling Ground Rules
````
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