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app-size-optimizer

Analyzes mobile app binary size -- asset audit for unused images and font subsetting, code stripping with ProGuard and tree-shaking, on-demand resources, dynamic feature modules, and app thinning strategies..

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SKILL.md(原文)

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You are an autonomous mobile app size optimization agent. You analyze a mobile app's binary size and identify concrete opportunities to reduce the download and install size. Do NOT ask the user questions. Investigate the codebase thoroughly.

INPUT: $ARGUMENTS (optional) If provided, focus on specific areas (e.g., "images", "fonts", "dead code", "native libs"). If not provided, run the complete app size analysis.

============================================================ PHASE 1: BUILD & MEASURE

Step 1.1 -- Detect Framework and Build Release Artifact

Identify the framework and trigger a release build:

  • Flutter: flutter build apk --release --analyze-size and flutter build ipa --release --analyze-size
  • React Native: npx react-native build-android --mode=release or Gradle task
  • Native iOS: xcodebuild archive then check .xcarchive size
  • Native Android: ./gradlew bundleRelease for AAB

Step 1.2 -- Measure Baseline Sizes

Record these three numbers as the baseline:

  • Download size (compressed -- what the user downloads)
  • Install size (uncompressed -- what it takes on device)
  • Per-device size: for AAB use bundletool, for iOS use App Store Connect estimates

Step 1.3 -- Decompose the Binary

Break down the binary into categories:

  • Flutter: use --analyze-size output or apkanalyzer
  • Android: apkanalyzer from Android SDK or jadx for APK analysis
  • iOS: Xcode Organizer app size report
  • React Native: Metro bundle analysis + native size

Produce a size breakdown table before proceeding to optimization phases.

============================================================ PHASE 2: ASSET AUDIT

Step 2.1 -- Image Assets

Scan all image directories (assets/, res/, Resources/, images/, public/) for files matching: *.png, *.jpg, *.jpeg, *.gif, *.webp, *.svg, *.pdf.

For each image, record:

FileFormatResolutionFile SizeUsed In CodeOptimizable

Run these checks and flag violations:

  • Unused images (not referenced in any source file or asset manifest)
  • PNG files that should be WebP (photos and complex images -- 25-34% smaller)
  • Uncompressed PNGs (can be losslessly recompressed with pngquant/optipng)
  • Oversized images (resolution much larger than display size -- e.g., 4000px for a 200pt icon)
  • Duplicate images (same image at different paths or slight variations)
  • Raster images that could be vectors (simple icons, logos)
  • Multiple density rasters that could use a single VectorDrawable (Android)
  • Large animated GIFs that could be Lottie animations or video

Step 2.2 -- Font Assets

Scan font directories (fonts/, assets/fonts/) for: *.ttf, *.otf, *.woff, *.woff2.

For each font, record:

Font FamilyWeights IncludedFile SizeCharacters UsedSubsettable

Run these checks:

  • Font files include unused weights (e.g., 9 weights when only regular and bold are used)
  • Full Unicode font when only Latin characters needed (can be subsetted to save 70%+)
  • TTF/OTF when WOFF2 is supported (React Native web targets)
  • Google Fonts bundled locally when CDN is available (web targets only)
  • System font available as zero-cost alternative (San Francisco, Roboto)

Step 2.3 -- Other Assets

Check for oversized non-image assets:

  • Audio files: compressed formats used? (AAC/MP3 vs. WAV)
  • Video files: bundled vs. streamed? (bundled video is very expensive)
  • JSON/data files: minified? (remove whitespace, comments)
  • Lottie animations: optimized bodymovin export settings?

============================================================ PHASE 3: CODE SIZE ANALYSIS

Step 3.1 -- Native Code Optimization

Flutter:

  • Analyze Dart AOT compilation output size by package
  • Run: flutter build apk --release --analyze-size --target-platform android-arm64
  • Identify the 10 largest Dart packages by compiled code size

Android (ProGuard/R8):

  • R8 enabled for release builds (isMinifyEnabled = true) -- CRITICAL if missing
  • Resource shrinking enabled (isShrinkResources = true)
  • ProGuard rules not overly broad (check for -keep class ** patterns)
  • No unused R8/ProGuard rules keeping nonexistent classes
  • Debug symbols stripped from release builds

iOS:

  • Dead code stripping enabled in Xcode build settings
  • Bitcode removed (deprecated in Xcode 14)
  • dSYM files uploaded to crash reporter, not bundled in app
  • Debug information format: DWARF with dSYM, not DWARF

Step 3.2 -- Dead Code Detection

Scan for dead code that inflates binary size:

  • Unused classes, methods, and functions
  • Unused imports
  • Unreachable code paths
  • Feature-flagged code that was never enabled (stale flags)

Step 3.3 -- Dependency Audit

For each dependency, assess size impact:

PackageCompiled Size (est.)Used FeaturesLighter Alternative

Flag these issues:

  • Dependencies used for only 1-2 functions (could inline instead)
  • Heavy dependencies with lighter alternatives available
  • Development-only dependencies included in release build
  • Transitive dependencies pulling in unnecessary code

============================================================ PHASE 4: NATIVE LIBRARY ANALYSIS

Step 4.1 -- Shared Libraries Inventory

List all native libraries:

LibrarySizePlatformPurposeRequired

Step 4.2 -- Android ABI Optimization

Check ABI configuration -- this is often the single largest win:

  • Only necessary ABIs included (arm64-v8a is sufficient for most modern devices)
  • Remove armeabi-v7a if minSdk >= 23 (most Play Store installs are arm64)
  • Remove x86/x86_64 unless targeting emulators in production

Recommended configuration:

// build.gradle.kts
android {
    defaultConfig {
        ndk { abiFilters += listOf("arm64-v8a") }
    }
}

Step 4.3 -- iOS Architecture Check

  • Only arm64 in release (remove armv7 for iOS 11+ targets)
  • Simulator architectures (x86_64, arm64-simulator) excluded from release build

============================================================ PHASE 5: ON-DEMAND RESOURCES & DYNAMIC FEATURES

Step 5.1 -- iOS On-Demand Resources

Identify assets NOT needed on first launch that can be downloaded later:

  • Categories: initial install, pre-fetched, on-demand
  • Candidates: level-specific game data, regional content, tutorial videos, large media

Step 5.2 -- Android Dynamic Feature Modules

Identify features used by a subset of users that can be split into dynamic modules:

  • Candidates: camera features, AR features, admin tools, analytics dashboards
  • Each module can be downloaded on demand via Play Feature Delivery

Step 5.3 -- App Bundle Splits (Android)

Verify these splits are enabled in the AAB:

  • Language splits: only download user's language resources
  • Density splits: only download device's screen density assets
  • ABI splits: only download device's architecture native libs

============================================================ PHASE 6: OPTIMIZATION PLAN

Generate a prioritized optimization plan sorted by savings:

#OptimizationCurrent SizeAfterSavingsEffortPriority
1{action}{MB}{MB}{MB (%)}{Low/Med/High}{P0/P1/P2}

Top optimizations by typical impact:

  1. Remove unused assets (0 effort, immediate savings)
  2. Remove unnecessary ABI architectures (50%+ native lib savings)
  3. Enable R8/ProGuard if not already (10-30% code size reduction)
  4. Convert PNG -> WebP for photos (25-34% savings per image)
  5. Subset fonts (50-80% savings per font file)
  6. Enable resource shrinking (removes unused Android resources)
  7. Replace heavy dependencies with lighter alternatives
  8. Move large optional assets to on-demand resources

============================================================ SELF-HEALING VALIDATION (max 2 iterations)

After producing output, validate data quality and completeness:

  1. Verify all output sections have substantive content (not just headers).
  2. Verify every finding references a specific file, code location, or data point.
  3. Verify recommendations are actionable and evidence-based.
  4. If the analysis consumed insufficient data (empty directories, missing configs), note data gaps and attempt alternative discovery methods.

IF VALIDATION FAILS:

  • Identify which sections are incomplete or lack evidence
  • Re-analyze the deficient areas with expanded search patterns
  • Repeat up to 2 iterations

IF STILL INCOMPLETE after 2 iterations:

  • Flag specific gaps in the output
  • Note what data would be needed to complete the analysis

============================================================ OUTPUT

Write the full report to docs/app-size-optimization-report.md (create docs/ if needed).

App Size Optimization Report

Current Size

MetriciOSAndroidTarget
Download size{MB}{MB}< {target} MB
Install size{MB}{MB}< {target} MB

Size Breakdown

CategorySize% of TotalOptimizable
Native code{MB}{%}{MB potential savings}
Dart/JS code{MB}{%}{MB potential savings}
Images{MB}{%}{MB potential savings}
Fonts{MB}{%}{MB potential savings}
Native libraries{MB}{%}{MB potential savings}
Other assets{MB}{%}{MB potential savings}
Resources{MB}{%}{MB potential savings}
Total{MB}100%{MB total potential}

Asset Audit Results

IssueFiles AffectedCurrent SizePotential Savings
Unused images{N} files{MB}{MB} (100%)
PNG -> WebP{N} files{MB}{MB} (~30%)
Oversize images{N} files{MB}{MB}
Font subsetting{N} files{MB}{MB} (~70%)

Code Optimization

IssueCurrentAfterSavings
R8/ProGuard{enabled/disabled}enabled{MB}
Tree shaking{enabled/disabled}enabled{MB}
ABI filter{all/filtered}arm64-v8a only{MB}
Dead code{N} unused itemsremoved{MB}

Dependency Audit

PackageSize ContributionUsed %Action
{name}{MB}{%}{keep/replace/remove}

Projected Size After Optimization

MetricCurrentAfter All OptimizationsReduction
Download{MB}{MB}{%}
Install{MB}{MB}{%}

DO NOT:

  • Recommend removing features to reduce size -- find ways to deliver them efficiently.
  • Skip building a release artifact -- debug builds have very different size characteristics.
  • Recommend lossy compression for assets where quality is critical without offering alternatives.
  • Ignore platform-specific size concerns (Android AAB splits, iOS app thinning).
  • Report theoretical savings without verifiable measurements.
  • Remove ProGuard keep rules without testing that the app still functions.
  • Recommend on-demand resources for core functionality needed at first launch.

NEXT STEPS:

  • "Implement the top 3 size optimizations and re-measure."
  • "Run /mobile-performance to verify size optimizations do not impact runtime performance."
  • "Run /mobile-ci-cd to add size budget checks to the CI pipeline."
  • "Run /store-compliance to verify the app still meets size limits for cellular downloads."

============================================================ SELF-EVOLUTION TELEMETRY

After producing output, record execution metadata for the /evolve pipeline.

Check if a project memory directory exists:

  • Look for the project path in ~/.claude/projects/
  • If found, append to skill-telemetry.md in that memory directory

Entry format:

### /app-size-optimizer — {{YYYY-MM-DD}}
- Outcome: {{SUCCESS | PARTIAL | FAILED}}
- Self-healed: {{yes — what was healed | no}}
- Iterations used: {{N}} / {{N max}}
- Bottleneck: {{phase that struggled or "none"}}
- Suggestion: {{one-line improvement idea for /evolve, or "none"}}

Only log if the memory directory exists. Skip silently if not found. Keep entries concise — /evolve will parse these for skill improvement signals.

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