instruments-profiling

---
name: instruments-profiling
description: Use when profiling native macOS or iOS apps with Instruments/xctrace. Covers correct binary selection, CLI arguments, exports, and common gotchas.
metadata:
  short-description: Instruments profiling for macOS/iOS apps
---

# Instruments Profiling (macOS/iOS)

Use this skill when the user wants performance profiling or stack analysis for native apps.
Focus: Time Profiler, `xctrace` CLI, and picking the correct binary/app instance.

## Quick Start (CLI)

- List templates: `xcrun xctrace list templates`
- Record Time Profiler (launch):
  - `xcrun xctrace record --template 'Time Profiler' --time-limit 60s --output /tmp/App.trace --launch -- /path/To/App.app`
- Record Time Profiler (attach):
  - Launch app yourself, get PID, then:
  - `xcrun xctrace record --template 'Time Profiler' --time-limit 60s --output /tmp/App.trace --attach <pid>`
- Open trace in Instruments:
  - `open -a Instruments /tmp/App.trace`

Note: `xcrun xctrace --help` is not a valid subcommand. Use `xcrun xctrace help record`.

## Picking the Correct Binary (Critical)

**Gotcha: Instruments may profile the wrong app** (e.g., one in `/Applications`) if LaunchServices resolves a different bundle.
Use these rules:

- Prefer direct binary path for deterministic launch:
  - `xcrun xctrace record ... --launch -- /path/App.app/Contents/MacOS/App`
- If launching `.app`, ensure it’s the intended bundle:
  - `open -n /path/App.app`
  - Verify with `ps -p <pid> -o comm= -o command=`
- If both `/Applications/App.app` and a local build exist, explicitly target the local build path.
- After launch, confirm the process path before trusting the trace.

## Command Arguments (xctrace)

- `--template 'Time Profiler'`: template name from `xctrace list templates`.
- `--launch -- <cmd>`: everything after `--` is the target command (binary or app bundle).
- `--attach <pid|name>`: attach to running process.
- `--output <path>`: `.trace` output. If omitted, file saved in CWD.
- `--