gc-mobile-ios

name	gc-mobile-ios
description	>- Use when this capability is needed.

Green Coding — iOS

Audit an iOS app for energy efficiency, battery impact, and sustainability.

When to use

• Auditing an iOS/iPadOS/watchOS app for energy consumption
• Investigating battery drain complaints
• Reviewing Swift/SwiftUI/UIKit code for green patterns
• Measuring SCI for a mobile operation (API call, screen render, background task)

MCP tools (optional)

If the sustainable-code MCP server is configured:

Tool	Purpose
sci_calculate	Compute SCI per mobile operation
grid_carbon_intensity	Get grid carbon intensity for user region
sci_compare	Compare SCI before/after optimization
creedengo_check	Check Swift files for energy-wasteful patterns

Workflow

iOS Green Audit Progress:
- [ ] Phase 1: Explore — understand architecture and energy profile
- [ ] Phase 2: Energy profiling — identify battery-draining operations
- [ ] Phase 3: Code patterns — check against Creedengo iOS rules
- [ ] Phase 4: Network efficiency — minimize data transfer
- [ ] Phase 5: Asset optimization — reduce resource footprint
- [ ] Phase 6: SCI measurement — quantify carbon per operation
- [ ] Phase 7: Report and recommendations

Phase 1 — Explore

Understand the app's architecture and energy profile:

• Language: Swift, Objective-C, or mixed?
• UI framework: SwiftUI, UIKit, or hybrid?
• Architecture: MVC, MVVM, TCA, VIPER?
• Dependencies: CocoaPods, SPM, Carthage? How many?
• Background tasks: push notifications, background fetch, location tracking?
• Network layer: URLSession, Alamofire, custom?
• Persistence: Core Data, SwiftData, Realm, SQLite, UserDefaults?
• Media: camera, video, audio processing?
• Sensors: GPS, accelerometer, Bluetooth, NFC?

Phase 2 — Energy profiling

Identify the biggest energy consumers. On iOS, the main energy drains are:

Component	Energy impact	What to check
Location Services	Very high	Continuous GPS vs significant-change vs visit monitoring
Networking	High	Request frequency, payload size, background transfers
CPU processing	High	Main thread blocking, inefficient algorithms, polling loops
Graphics/GPU	High	Overdraw, off-screen rendering, animation complexity
Bluetooth/sensors	Medium-high	Polling frequency, unnecessary scans
Display	Medium	Brightness APIs, always-on content, dark mode support
Background tasks	Medium	BGTaskScheduler usage, background refresh frequency

Measurement tools

Recommend the user profile their app using:

1. Xcode Energy Gauge (Product → Profile → Energy Impact) — real-time energy score (0-20 scale) during development
2. Xcode Instruments — Energy Log — detailed per-subsystem breakdown (CPU, GPU, network, location, Bluetooth)
3. MetricKit — production energy metrics from real users (iOS 13+):

   // Add MXMetricManagerSubscriber to receive daily energy reports
   class MetricsSubscriber: NSObject, MXMetricManagerSubscriber {
       func didReceive(_ payloads: [MXMetricPayload]) {
           // payloads contain cumulativeCellularConditionTime,
           // cumulativeWiFiConditionTime, cpuMetrics, gpuMetrics
       }
   }
   

4. Xcode Organizer → Energy — aggregated energy data from App Store users

Phase 3 — Code patterns (Creedengo iOS rules)

Check Swift files against Creedengo iOS energy rules:

Rule	Pattern to avoid	Green alternative
Location precision	kCLLocationAccuracyBest when not needed	Use kCLLocationAccuracyHundredMeters or CLLocationManager.significantLocationChangeMonitoringAvailable()
Location continuous	startUpdatingLocation() running permanently	Use startMonitoringSignificantLocationChanges() or requestLocation() for one-shot
Sensor polling	Timer-based accelerometer/gyroscope reads	Use CMMotionManager with appropriate updateInterval, stop when not needed
Idle timer	UIApplication.shared.isIdleTimerDisabled = true	Only disable when genuinely needed (navigation, video playback), re-enable promptly
Brightness override	Setting UIScreen.main.brightness to max	Let the system manage brightness, respect auto-brightness
Torch/flashlight	AVCaptureDevice.torchMode = .on left on	Turn off torch as soon as task completes
Animation overuse	Complex UIView.animate chains, always-running CADisplayLink	Use UIView.animate with prefers-reduced-motion check, avoid continuous animations
Bluetooth scanning	centralManager.scanForPeripherals without timeout	Set a scan timeout, stop scanning once device found
Background fetch	Aggressive setMinimumBackgroundFetchInterval	Use BGAppRefreshTaskRequest with reasonable earliest begin date
Large image loading	Loading full-resolution images into memory	Use UIImage(contentsOfFile:) with downsampling, or ImageIO for thumbnails

Use the creedengo_check MCP tool on Swift files, or manually review against these patterns.

Additionally check for general Swift energy patterns:

• Prefer struct over class — value types avoid heap allocation and ARC overhead
• Avoid DispatchQueue.main.async flooding — batch UI updates
• Use lazy var for expensive computed properties
• Prefer async/await over completion handler chains — cleaner, avoids retain cycles
• Use URLSession background transfers for large downloads instead of foreground requests

Phase 4 — Network efficiency

Mobile network operations are energy-expensive. Check:

Check	Why it matters
Batch API calls	Each network transaction wakes the radio. Batch multiple requests into one
Compress payloads	Use gzip/brotli. Consider Protocol Buffers or MessagePack over JSON for high-frequency APIs
Cache aggressively	Use URLCache with appropriate policies. Cache images with NSCache or third-party (Kingfisher, SDWebImage)
Avoid polling	Replace polling with push notifications (APNs) or WebSocket for real-time updates
Background transfers	Use URLSessionConfiguration.background for non-urgent uploads/downloads — iOS batches these efficiently
Prefetch intelligently	Use UITableViewDataSourcePrefetching / UICollectionViewDataSourcePrefetching — don't prefetch everything
Reduce image sizes	Request appropriate resolution from server (?w=375 for phone, ?w=768 for tablet)
HTTP caching headers	Ensure ETag, Last-Modified, Cache-Control are set server-side

Phase 5 — Asset optimization

Asset type	Check	Target
Images	HEIC preferred over PNG/JPEG. Use Asset Catalog with device-specific variants	Smallest format for quality needed
App size	App Thinning enabled? Bitcode? On-demand resources for large assets?	Smaller download = less energy to transfer
Fonts	System fonts (SF Pro, SF Mono) preferred over custom fonts	Zero download cost for system fonts
Videos	HLS adaptive streaming? Appropriate resolution per device?	Don't stream 4K to an iPhone SE
Core Data	Batch inserts (NSBatchInsertRequest)? Proper indexing? Fetch limits?	Reduce disk I/O and CPU
Launch time	Minimize work in application(_:didFinishLaunchingWithOptions:)	Faster launch = less energy

Phase 6 — SCI measurement

Measure the carbon intensity of key operations:

1. Choose functional units: "per API call", "per screen render", "per background sync"
2. Measure wall-clock time using CFAbsoluteTimeGetCurrent() or ContinuousClock:

   let clock = ContinuousClock()
   let duration = try await clock.measure {
       // operation to measure
   }
   let wallTimeMs = duration.components.seconds * 1000
       + duration.components.attoseconds / 1_000_000_000_000_000
   

3. Get grid carbon intensity via grid_carbon_intensity MCP tool (use user's region)
4. Calculate SCI via sci_calculate MCP tool:
   • wallTimeMs: measured duration
   • devicePowerW: ~3W (iPhone average) or ~5W (iPad)
   • carbonIntensity: from step 3
   • embodiedTotalG: ~70000 (iPhone, from Apple Environmental Report)
   • lifetimeHours: ~26280 (3 years typical iPhone lifecycle)

Phase 7 — Report

## iOS Green Audit: [app name]

### Energy profile
| Component | Impact | Status | Notes |
|-----------|--------|--------|-------|
| Location | high/medium/low/none | ok/warn/fail | ... |
| Networking | ... | ... | ... |
| CPU/processing | ... | ... | ... |
| Graphics/GPU | ... | ... | ... |
| Sensors | ... | ... | ... |
| Background tasks | ... | ... | ... |

### Code patterns (Creedengo iOS)
| File | Rule violated | Severity | Fix |
|------|--------------|----------|-----|
| ... | ... | high/medium/low | ... |

### SCI measurements
| Operation | SCI (mgCO2eq) | Notes |
|-----------|---------------|-------|
| ... | ... | ... |

### Top 5 Recommendations
1. [highest impact action]
2. ...

### Methodology and sources
- Formula: SCI = ((E x I) + M) / R — [GSF SCI Specification v1.0](https://sci-guide.greensoftware.foundation/) (ISO 21031:2024)
- Code rules: [Creedengo iOS](https://github.com/green-code-initiative/creedengo-ios) — green-code-initiative
- Energy profiling: Xcode Instruments Energy Log / MetricKit
- Device power: [value] W — Apple Product Environmental Report [year]
- Embodied carbon: [value] gCO2eq — [Apple Product Environmental Report](https://www.apple.com/environment/) [year]
- Grid carbon intensity: [value] gCO2eq/kWh — [Ember Global Electricity Review](https://ember-energy.org/) [year]
- Platform guide: [Apple Energy Efficiency Guide for iOS Apps](https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/)

Gotchas

• Xcode Energy Gauge is not available in simulators: Energy profiling requires a physical device. Always test energy on real hardware, not the iOS Simulator.
• MetricKit reports are daily aggregates: You cannot get real-time energy data from MetricKit. For granular measurement during development, use Xcode Instruments instead.
• Battery percentage is not a valid energy metric: Battery drain depends on total capacity, charge cycles, ambient temperature, and other apps. Use Xcode's energy score (0-20) or MetricKit cumulative metrics instead.
• Background app refresh varies by user settings: Users can disable background refresh per-app. Don't assume your background tasks always run — and don't over-schedule as backup.

Post-report verification

After presenting the iOS audit report, automatically run /gc-verify in quick mode. This triggers a Chain-of-Verification (CoVe) process: extract claims from the report, generate adversarial questions, answer each independently, and present findings under a ## Verification (CoVe) heading.

Related commands

• /gc-mobile-android — green coding audit for Android apps
• /gc-setup — full 9-phase sustainability audit (web-focused)
• /gc-measure-sci — measure SCI for any operation
• /gc-dev — daily development companion

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Source: fullo/sustainable-code-skill-setup — distributed by TomeVault.