Codex++ iOS Simulator Tweak

Skill by ara.so — Codex Skills collection.

A Codex++ tweak that adds an iOS Simulator tab to Codex's right panel. It mirrors a booted iOS simulator without opening Simulator.app, forwards touch and keyboard input, and lets you annotate simulator UI elements directly into Codex comments.

What It Does

• Embeds a live iOS simulator view in Codex's right panel
• Mirrors simulator output through CoreSimulator IOSurface (headless)
• Forwards touch, drag, swipe, keyboard, and hardware button input
• Provides UI element annotations using the accessibility tree
• Device picker to switch between installed simulators
• Auto-boot capability when no simulator is running
• Screenshot and hardware control (Home, Lock, Side Button, Siri)

Installation

Prerequisites

1. macOS with full Xcode installed (not just Command Line Tools)
2. At least one iOS simulator runtime/device downloaded
3. Xcode command-line tools properly configured:

sudo xcode-select -s /Applications/Xcode.app

Verify Xcode path:

xcode-select -p
# Should output: /Applications/Xcode.app/Contents/Developer

Install Codex++

First install Codex++, the Codex extension framework.

Install the Tweak

Clone or download this tweak into the Codex++ tweaks directory:

mkdir -p ~/Library/Application\ Support/codex-plusplus/tweaks/
cd ~/Library/Application\ Support/codex-plusplus/tweaks/
git clone https://github.com/b-nnett/codex-plusplus-ios-simulator.git ios-simulator

Or manually place the folder:

~/Library/Application Support/codex-plusplus/tweaks/ios-simulator/

The tweak runs a preflight check on first launch and shows fix hints if dependencies are missing.

Usage

Opening the Simulator Panel

Via UI:

• Click the + menu in Codex's right panel
• Select iOS Simulator (appears below the divider)

Via Keyboard:

• Press Cmd+Y

Controls

Once the panel is open:

• Tap/Click: Click anywhere on the simulator screen
• Drag/Swipe: Click and drag
• Keyboard: Type directly (focus is captured)
• Hardware Buttons:
  • Home button
  • Lock button
  • Side button
  • Siri button
• Screenshot: Capture current simulator state
• Device Picker: Dropdown to switch simulators
• Auto-boot: Toggle to automatically boot simulator when none is running

Annotations

Annotation mode allows you to reference specific UI elements in Codex comments:

1. Click the annotation button in the simulator panel
2. Click on a UI element in the simulator
3. Write your comment in Codex's native comment UI

The tweak automatically includes:

• Element label and accessibility role
• Simulator device ID
• Element frame coordinates
• Marker point
• Viewport size

Example annotation payload:

{
  "element": {
    "label": "Sign In",
    "role": "Button",
    "frame": { "x": 120, "y": 450, "width": 175, "height": 44 }
  },
  "simulator": "iPhone 15 Pro",
  "marker": { "x": 207.5, "y": 472 },
  "viewport": { "width": 393, "height": 852 }
}

Use cases:

• "Fix this button layout" → points to specific button
• "Why is this label truncated?" → includes label frame and text
• "Adjust spacing here" → marks exact coordinates

File Structure

ios-simulator/
├── index.js                    # Main Codex++ tweak entry point
├── helpers/
│   ├── sim-capture.swift       # Headless frame capture helper
│   └── sim-input.m             # Touch, keyboard, hardware button helper
├── manifest.json               # Tweak metadata
└── README.md

Key Code Patterns

Tweak Entry Point (index.js)

The main tweak file exports a Codex++ tweak object:

module.exports = {
  name: 'iOS Simulator',
  icon: 'phone.fill',
  
  // Called when panel is opened
  onActivate(panel) {
    panel.setTitle('iOS Simulator');
    initializeSimulator(panel);
  },
  
  // Called when panel is closed
  onDeactivate() {
    stopHelpers();
    cleanupResources();
  },
  
  // Panel UI setup
  renderPanel(container) {
    const canvas = document.createElement('canvas');
    const controls = createControlBar();
    container.append(canvas, controls);
    return { canvas, controls };
  }
};

Capturing Simulator Frames (sim-capture.swift)

The Swift helper uses CoreSimulator to capture IOSurface frames:

import Foundation
import CoreSimulator
import IOSurface

// Connect to simulator framebuffer
let device = SimDevice(udid: deviceUDID)
let surface = device.surface // IOSurface

// Capture loop
while isRunning {
    let surfaceRef = device.io.surface
    let baseAddress = IOSurfaceGetBaseAddress(surfaceRef)
    let width = IOSurfaceGetWidth(surfaceRef)
    let height = IOSurfaceGetHeight(surfaceRef)
    
    // Write raw frame to stdout
    fwrite(baseAddress, 1, width * height * 4, stdout)
    fflush(stdout)
    
    usleep(16667) // ~60fps
}

Sending Input Events (sim-input.m)

The Objective-C helper sends touch and keyboard events:

#import <Foundation/Foundation.h>
#import <SimulatorKit/SimulatorKit.h>

// Send touch event
- (void)sendTouchAtX:(CGFloat)x y:(CGFloat)y phase:(NSString*)phase {
    SimDevice *device = [self deviceWithUDID:deviceUDID];
    SimDeviceIOClient *io = device.io;
    
    SimDeviceIOTouchEvent *event = [SimDeviceIOTouchEvent new];
    event.x = x;
    event.y = y;
    event.phase = [self phaseFromString:phase]; // began, moved, ended
    
    [io sendTouchEvent:event];
}

// Send keyboard input
- (void)sendKeyPress:(NSString*)key {
    SimDevice *device = [self deviceWithUDID:deviceUDID];
    [device.io sendKeyboardEvent:key];
}

// Hardware buttons
- (void)pressHomeButton {
    SimDevice *device = [self deviceWithUDID:deviceUDID];
    [device.io pressButton:SimDeviceIOButtonHome];
}

Device Management

List available simulators:

const { execSync } = require('child_process');

function getAvailableSimulators() {
  const output = execSync('xcrun simctl list devices --json', { encoding: 'utf8' });
  const data = JSON.parse(output);
  
  const devices = [];
  for (const runtime in data.devices) {
    for (const device of data.devices[runtime]) {
      if (device.isAvailable) {
        devices.push({
          udid: device.udid,
          name: device.name,
          state: device.state,
          runtime: runtime
        });
      }
    }
  }
  return devices;
}

Boot a simulator:

function bootSimulator(udid) {
  execSync(`xcrun simctl boot ${udid}`, { encoding: 'utf8' });
}

Shutdown:

function shutdownSimulator(udid) {
  execSync(`xcrun simctl shutdown ${udid}`, { encoding: 'utf8' });
}

Configuration

The tweak compiles helper binaries on first use and caches them:

~/Library/Caches/co.bennett.ios-simulator/
├── sim-capture          # Compiled Swift helper
└── sim-input            # Compiled Objective-C helper

No network requests are made. All compilation happens locally.

manifest.json

{
  "name": "iOS Simulator",
  "version": "1.0.0",
  "description": "Headless iOS Simulator for Codex++",
  "entry": "index.js",
  "permissions": [
    "process",
    "filesystem"
  ],
  "shortcuts": [
    {
      "key": "cmd+y",
      "action": "toggleSimulator"
    }
  ]
}

Troubleshooting

Preflight Check Failed

Error: "Xcode not found"

# Ensure Xcode is installed
xcode-select -p

# If pointing to Command Line Tools, fix with:
sudo xcode-select -s /Applications/Xcode.app

Error: "No simulators available"

# List available simulators
xcrun simctl list devices

# Download iOS runtimes in Xcode:
# Xcode → Settings → Platforms → [Download iOS runtime]

Helper Compilation Fails

Error: "Swift compiler not found"

# Verify swiftc is available
which swiftc

# Should be under Xcode.app/Contents/Developer/
# If not, run: sudo xcode-select -s /Applications/Xcode.app

Error: "Framework not found: SimulatorKit"

# SimulatorKit is a private framework included with Xcode
# Ensure full Xcode is installed, not just Command Line Tools

# Check framework exists:
ls /Applications/Xcode.app/Contents/Developer/Library/PrivateFrameworks/SimulatorKit.framework

Simulator Won't Boot

Error: "Unable to boot device in current state: Booted"

The simulator is already running. Use the device picker to select it, or shut it down first:

xcrun simctl shutdown <UDID>

Error: "Failed to boot device"

Check simulator logs:

xcrun simctl spawn booted log stream --predicate 'subsystem == "com.apple.CoreSimulator"'

No Frame Output

Symptom: Black screen in Codex panel

1. Verify simulator is booted:

   xcrun simctl list devices | grep Booted
   

2. Check helper process is running:

   ps aux | grep sim-capture
   

3. Restart the panel (close and reopen with Cmd+Y)

Touch Input Not Working

1. Ensure simulator window is not open in Simulator.app (conflicting input)
2. Check sim-input helper is running:

   ps aux | grep sim-input
   

3. Verify device UDID matches between capture and input helpers

Annotations Return Empty Labels

Cause: App under test has poor accessibility labeling

Solution: Add accessibility labels to your UI elements:

// SwiftUI
Text("Sign In")
    .accessibilityLabel("Sign In Button")
    .accessibilityIdentifier("signInButton")

// UIKit
button.accessibilityLabel = "Sign In Button"
button.accessibilityIdentifier = "signInButton"

Common Workflows

Testing a SwiftUI App

1. Open simulator panel (Cmd+Y)
2. Select device from picker (e.g., "iPhone 15 Pro")
3. Launch your app from Xcode or command line:

   xcrun simctl launch <UDID> com.yourcompany.yourapp
   

4. Interact with UI in Codex panel
5. Annotate elements to document issues

Debugging Layout Issues

1. Enable annotation mode
2. Click on the element with incorrect layout
3. Write comment: "This button is clipped on iPhone SE"
4. The annotation includes frame and viewport size for the agent to analyze

Recording Interaction Sequences

// Custom extension to record touch sequences
const touches = [];

panel.on('touch', (x, y, phase) => {
  touches.push({ x, y, phase, timestamp: Date.now() });
});

panel.on('annotate', () => {
  // Include touch sequence in annotation
  return { touches, viewport, element };
});

Privacy & Security

• No Screen Recording permission required (uses CoreSimulator IOSurface directly)
• No network requests (all helpers compiled locally)
• Helper processes stopped when tweak deactivates
• Cached binaries stored in user cache directory only

License

MIT