Simulator Workflows

Use the execute_simulator_command MCP tool for all simulator management

The xclaude-plugin provides the execute_simulator_command MCP tool which consolidates all simctl operations into a single, token-efficient dispatcher.

⚠️ CRITICAL: Always Use MCP Tools First

This is the most important rule: When working with iOS simulators, you MUST use the execute_simulator_command MCP tool.

• ✅ DO: Invoke execute_simulator_command for all device/app lifecycle operations
• ✅ DO: If the MCP tool fails, adjust parameters and retry
• ✅ DO: Read error messages and debug the parameters
• ❌ NEVER: Fall back to bash xcrun simctl commands
• ❌ NEVER: Use simctl directly in bash
• ❌ NEVER: Run xcrun simctl commands in a terminal

Why? The MCP tool provides:

• Structured error handling
• Token efficiency (consolidated into 1 tool vs. verbose bash output)
• Proper integration with the xclaude-plugin architecture
• Consistent response formatting

If execute_simulator_command fails, the issue is with parameters or device state - not that you should use bash.

When to Use Bash (And When NOT to)

❌ NEVER Use Bash For These (Use MCP Tools Instead)

Task	❌ WRONG (Bash)	✅ RIGHT (MCP Tool)
List devices	xcrun simctl list	execute_simulator_command op: "list"
Boot simulator	xcrun simctl boot <UDID>	execute_simulator_command op: "device-lifecycle" sub: "boot"
Install app	xcrun simctl install <UDID> <app.app>	execute_simulator_command op: "app-lifecycle" sub: "install"
Launch app	xcrun simctl launch <UDID> <bundle-id>	execute_simulator_command op: "app-lifecycle" sub: "launch"
Screenshot	xcrun simctl io <UDID> screenshot	execute_simulator_command op: "io" sub: "screenshot"

✅ Bash is Acceptable For (Non-Simulator Tasks)

• File operations: mkdir, cp, rm, ls, etc.
• Text inspection: grep, find, cat, etc.
• Git operations: git status, git log, etc.
• Environment checks: which, simctl --version, etc.
• Project exploration: find . -name "*.app", etc.

The Rule: If it's about simulator management → Use MCP tool, not bash

Quick Reference

Task	MCP Tool	Operation	Sub-Operation
List devices	execute_simulator_command	list	-
Boot device	execute_simulator_command	device-lifecycle	boot
Shutdown device	execute_simulator_command	device-lifecycle	shutdown
Create device	execute_simulator_command	device-lifecycle	create
Delete device	execute_simulator_command	device-lifecycle	delete
Install app	execute_simulator_command	app-lifecycle	install
Launch app	execute_simulator_command	app-lifecycle	launch
Screenshot	execute_simulator_command	io	screenshot
Health check	execute_simulator_command	health-check	-

Device Management

1. Listing Devices - Use execute_simulator_command with operation: "list"

Invoke the execute_simulator_command MCP tool:

{
  "operation": "list"
}

Returns (Progressive Disclosure):

{
  "summary": {
    "total_devices": 47,
    "available_devices": 31,
    "booted_devices": 1
  },
  "booted": [
    {
      "name": "iPhone 15",
      "udid": "ABC123...",
      "state": "Booted",
      "runtime": "iOS 17.0"
    }
  ],
  "cache_id": "sim-list-xyz789",
  "next_steps": [
    "Use device name or UDID for operations",
    "Query cache_id for full device list if needed"
  ]
}

Note: Large device lists use progressive disclosure to save tokens.

2. Booting a Simulator - Use execute_simulator_command with device-lifecycle

Invoke the execute_simulator_command MCP tool:

By Name:

{
  "operation": "device-lifecycle",
  "sub_operation": "boot",
  "device_id": "iPhone 15"
}

By UDID:

{
  "operation": "device-lifecycle",
  "sub_operation": "boot",
  "device_id": "ABC123-DEF456-...",
  "parameters": {
    "wait_for_boot": true
  }
}

wait_for_boot: Blocks until device fully booted (recommended)

3. Shutting Down

{
  "operation": "device-lifecycle",
  "sub_operation": "shutdown",
  "device_id": "iPhone 15"
}

4. Creating a New Simulator

{
  "operation": "device-lifecycle",
  "sub_operation": "create",
  "device_id": "My iPhone 15 Test",
  "parameters": {
    "device_type": "iPhone 15",
    "runtime": "iOS 17.0"
  }
}

Returns: New device UDID

Available Device Types:

• iPhone SE (3rd generation)
• iPhone 14, 14 Plus, 14 Pro, 14 Pro Max
• iPhone 15, 15 Plus, 15 Pro, 15 Pro Max
• iPad (10th generation), iPad Air, iPad Pro

Check available runtimes: Use list to see installed iOS versions

5. Deleting a Simulator

{
  "operation": "device-lifecycle",
  "sub_operation": "delete",
  "device_id": "My iPhone 15 Test"
}

Warning: This is permanent and cannot be undone.

6. Erasing a Simulator

Remove all data but keep device:

{
  "operation": "device-lifecycle",
  "sub_operation": "erase",
  "device_id": "iPhone 15"
}

When to erase:

• Reset app state completely
• Clear test data
• Reproduce fresh install behavior

7. Cloning a Simulator

Duplicate a device with all its data:

{
  "operation": "device-lifecycle",
  "sub_operation": "clone",
  "device_id": "iPhone 15",
  "parameters": {
    "new_name": "iPhone 15 Clone"
  }
}

Use case: Preserve a specific test state

App Management

1. Installing an App

{
  "operation": "app-lifecycle",
  "sub_operation": "install",
  "device_id": "iPhone 15",
  "app_identifier": "/path/to/MyApp.app"
}

Note: app_identifier is the path to .app bundle for install operation.

Build + Install Pattern:

1. execute_xcode_command (operation: build) → Get .app path
2. execute_simulator_command (operation: app-lifecycle, sub_operation: install)

2. Launching an App

{
  "operation": "app-lifecycle",
  "sub_operation": "launch",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp"
}

With Arguments:

{
  "operation": "app-lifecycle",
  "sub_operation": "launch",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp",
  "parameters": {
    "arguments": ["--test-mode", "--mock-data"],
    "environment": {
      "API_URL": "https://staging.example.com"
    }
  }
}

3. Terminating an App

{
  "operation": "app-lifecycle",
  "sub_operation": "terminate",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp"
}

4. Uninstalling an App

{
  "operation": "app-lifecycle",
  "sub_operation": "uninstall",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp"
}

5. Getting App Container Paths

For accessing app data:

{
  "operation": "get-app-container",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp",
  "parameters": {
    "container_type": "data"
  }
}

Container Types:

• data: App's Documents, Library, tmp directories
• bundle: App's .app bundle
• group: Shared group containers

Returns: File system path to container

Use case: Inspect database files, logs, or user defaults

Capture & Media

1. Taking Screenshots

{
  "operation": "io",
  "sub_operation": "screenshot",
  "device_id": "iPhone 15",
  "parameters": {
    "output_path": "/path/to/screenshot.png"
  }
}

Auto-generated path: If output_path omitted, creates temp file

2. Recording Video

{
  "operation": "io",
  "sub_operation": "video",
  "device_id": "iPhone 15",
  "parameters": {
    "output_path": "/path/to/video.mp4",
    "duration": 30
  }
}

Note: Duration in seconds. Press Ctrl+C to stop recording manually.

Advanced Operations

1. Opening URLs

{
  "operation": "openurl",
  "device_id": "iPhone 15",
  "parameters": {
    "url": "myapp://deep-link/path"
  }
}

Use cases:

• Test universal links
• Test deep linking
• Open Safari to specific URL

2. Push Notifications

{
  "operation": "push",
  "device_id": "iPhone 15",
  "app_identifier": "com.example.MyApp",
  "parameters": {
    "payload": {
      "aps": {
        "alert": "Test notification",
        "badge": 1,
        "sound": "default"
      }
    }
  }
}

Payload: Standard APNs JSON payload

Environment Validation

Health Check

Verify iOS development environment:

{
  "operation": "health-check"
}

Checks:

• Xcode installation
• Command line tools
• simctl availability
• CoreSimulator framework

Returns:

{
  "xcode_installed": true,
  "xcode_version": "15.0",
  "simctl_available": true,
  "issues": []
}

Device Selection Strategies

By Name (Easiest)

{
  "device_id": "iPhone 15"
}

Pro: Readable, easy to remember Con: May match multiple devices

By UDID (Most Reliable)

{
  "device_id": "ABC123-DEF456-GHI789..."
}

Pro: Unique, guaranteed single match Con: Long, hard to remember

Using "booted" (Convenience)

Some tools (like IDB) accept "booted" to target the currently booted simulator:

{
  "target": "booted"
}

Note: Only works with IDB operations, not simctl

Common Workflows

Workflow: Fresh Install Test

1. boot → Start simulator
2. uninstall → Remove existing app
3. install → Install fresh build
4. launch → Start app
5. (UI automation) → Test flow
6. terminate → Stop app
7. shutdown → Stop simulator

Workflow: Rapid Iteration

1. build → Compile latest code
2. install → Update app on simulator (already booted)
3. terminate → Stop running app
4. launch → Start updated app

Note: No need to boot/shutdown between iterations

Workflow: Multi-Device Testing

1. list → Get available devices
2. For each device:
   - boot → Start device
   - install → Install app
   - launch → Start app
   - (run tests) → Execute test suite
   - terminate → Stop app
   - shutdown → Stop device

Troubleshooting

Device Not Found

Problem: "Unable to find device: iPhone 15"

Solutions:

1. Run list to see exact device names
2. Use UDID instead of name
3. Check device hasn't been deleted

Unable to Boot

Problem: Boot fails or times out

Solutions:

1. Check disk space (simulators need space)
2. Shutdown other running simulators
3. Restart CoreSimulator: killall -9 com.apple.CoreSimulator.CoreSimulatorService
4. Run health-check to validate environment

App Install Fails

Problem: Install operation fails

Solutions:

1. Verify .app path is correct
2. Check device is booted
3. Ensure .app is built for simulator (not device)
4. Try erasing simulator first

App Won't Launch

Problem: Launch succeeds but app crashes immediately

Solutions:

1. Check app logs in Console.app
2. Verify app is signed correctly
3. Check for missing frameworks/resources
4. Try clean build + reinstall

Performance Tips

1. Keep Simulators Booted

Booting is slow (~5-10 seconds). Keep simulator running during development.

2. Use Progressive Disclosure

Device lists can be large. Summary provides what you need 95% of the time.

3. Reuse Simulators

Creating/deleting is slower than erasing. Reuse devices when possible.

4. Parallel Operations

Boot multiple simulators in parallel for multi-device testing:

Launch 3 boot operations concurrently
Wait for all to complete
Proceed with testing

Integration with Other Tools

With Xcodebuild

1. execute_xcode_command (build) → Get .app bundle
2. execute_simulator_command (install) → Install to simulator
3. execute_simulator_command (launch) → Start app

With IDB

1. execute_simulator_command (boot) → Start device
2. execute_idb_command (describe) → Query UI
3. execute_idb_command (tap) → Interact

With Testing

1. execute_simulator_command (boot) → Start device
2. execute_xcode_command (test) → Run tests on device
3. execute_simulator_command (shutdown) → Stop device

Integration with MCP Tools

This Skill works with execute_simulator_command tool:

• All operations use the execute_simulator_command tool
• Tool handles simctl execution
• Tool provides progressive disclosure for large outputs
• This Skill teaches WHEN and HOW to use operations

Related Skills

• xcode-workflows: Building apps for simulators
• ui-automation-workflows: Automating simulator interactions
• ios-testing-patterns: Test execution strategies

Related Resources

• xc://operations/simulator: Complete simctl operations reference
• xc://reference/device-specs: Available device types and runtimes
• xc://reference/error-codes: Common simulator errors

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Tip: Use list to discover, boot by name for convenience, use UDID for reliability.