Android Reverse Engineering & API Extraction

A skill for Claude Code and Cursor that decompiles Android APK/XAPK/JAR/AAR files and extracts the HTTP APIs used by the app (Retrofit endpoints, OkHttp calls, hardcoded URLs, authentication patterns) so you can document and reproduce them without the original source code.

First-class Kotlin support: modern Android apps are Kotlin/KMP, heavily obfuscated with R8. This skill recovers the original Kotlin class names from metadata R8 cannot strip, and extracts APIs from Ktor, Apollo (GraphQL) and Koin, not just the classic Retrofit/OkHttp stack. See Kotlin name recovery below.

Cross-platform scripts: Bash scripts on Linux/macOS and native PowerShell (*.ps1) on Windows cover the full workflow: fingerprint, decompile, API extraction, and Kotlin name recovery. See Usage for examples on each platform.

Table of Contents

• What it does
• Requirements
• Installation
  • Claude Code
  • Cursor
• Usage
• Repository Structure
• References
• Acknowledgments
• Disclaimer
• License

What it does

Capability	Description
Fingerprint first (Phase 0)	Triage an APK/XAPK in seconds: detect the framework (Flutter / React Native / Cordova / Xamarin / native-Kotlin), HTTP stack, obfuscation level and native libs before spending time on a full decompile
Decompile	APK, XAPK, JAR, and AAR files using jadx and Fernflower/Vineflower (single engine or side-by-side comparison)
Recover Kotlin names	Rebuild original *Repository / *ViewModel / *UseCase class names from R8-obfuscated binaries using Kotlin metadata that R8 cannot strip
Extract APIs	Retrofit, OkHttp, Volley and modern Kotlin/KMP stacks: Ktor, Apollo (GraphQL), Koin DI; endpoints, hardcoded URLs, auth headers, tokens and HMAC request-signing schemes
Trace call flows	From Activities/Fragments through ViewModels and repositories down to HTTP calls
Analyze structure	Manifest, packages, architecture patterns
Handle obfuscation	R8-resistant path/URL extraction plus strategies for navigating ProGuard/R8 output

Requirements

Required:

• Java JDK 17+
• jadx (CLI)

Optional (recommended):

• Vineflower or Fernflower: better output on complex Java code
• dex2jar: needed to use Fernflower on APK/DEX files

See plugins/android-reverse-engineering/skills/android-reverse-engineering/references/setup-guide.md for detailed installation instructions.

Installation

Claude Code

From GitHub (recommended)

Inside Claude Code, run:

/plugin marketplace add SimoneAvogadro/android-reverse-engineering-skill
/plugin install android-reverse-engineering@android-reverse-engineering-skill

The skill will be permanently available in all future sessions.

From a local clone

git clone https://github.com/SimoneAvogadro/android-reverse-engineering-skill.git

Then in Claude Code:

/plugin marketplace add /path/to/android-reverse-engineering-skill
/plugin install android-reverse-engineering@android-reverse-engineering-skill

Cursor

Cursor loads project skills from .cursor/skills/ in the workspace root — the folder you open in Cursor, not every repo on disk.

Clone this repository, then pick one setup:

Goal	What to do
Use the skill here (simplest)	Open this repo as your Cursor workspace. Put APKs anywhere on disk and reference them by path.
Use the skill in another project	Copy (or git submodule) both .cursor/skills/android-reverse-engineering/ and plugins/android-reverse-engineering/ into that project's repo root, then open that project in Cursor. The skill's SKILL.md references scripts under plugins/… relative to the workspace root — copying only SKILL.md is not enough.
Both projects at once	Add this repo and your other project to a multi-root workspace.
All projects (advanced)	Install under ~/.cursor/skills/android-reverse-engineering/, but adjust script paths in SKILL.md to a fixed location on disk (e.g. where you cloned this repo).

The project skill lives at .cursor/skills/android-reverse-engineering/ and points to the shared scripts under plugins/android-reverse-engineering/skills/android-reverse-engineering/.

1. Ensure Java 17+, jadx, and optionally dex2jar / Vineflower are on your PATH (see setup-guide).
2. Verify dependencies (run from the workspace root that contains plugins/):
   • Linux / macOS: bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/check-deps.sh
   • Windows: & plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/check-deps.ps1
3. Invoke via @android-reverse-engineering or phrases like "decompile this APK".

Unlike Claude Code, Cursor has no global /plugin install — the skill is available only in workspaces where .cursor/skills/android-reverse-engineering/ is present (unless you use the personal-skill path above).

Usage

Slash command

/decompile path/to/app.apk

This runs the full workflow: dependency check, decompilation, and initial structure analysis.

Natural language

The skill activates on phrases like:

• "Decompile this APK"
• "Reverse engineer this Android app"
• "Extract API endpoints from this app"
• "Follow the call flow from LoginActivity"
• "Analyze this AAR library"

Manual scripts (bash on Linux/macOS)

# Check dependencies
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/check-deps.sh

# Install a missing dependency (auto-detects OS and package manager)
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/install-dep.sh jadx
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/install-dep.sh vineflower

# Fingerprint an APK/XAPK BEFORE decompiling (Phase 0 triage):
# framework, HTTP stack, obfuscation level, native libs, notable SDKs
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/fingerprint.sh app.apk

# Decompile APK with jadx (default)
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh app.apk

# Decompile XAPK (auto-extracts and decompiles each APK inside)
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh app-bundle.xapk

# Decompile with Fernflower
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh --engine fernflower library.jar

# Run both engines and compare
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh --engine both --deobf app.apk

# Find API calls (defaults to a full scan across every supported stack)
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --retrofit
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --urls

# Modern Kotlin/KMP stacks and obfuscation-resistant extraction
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --ktor    # Ktor client
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --apollo  # Apollo / GraphQL
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --paths   # quoted path literals that survive R8 inlining

Manual scripts (PowerShell on Windows)

# Check dependencies
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/check-deps.ps1

# Fingerprint before decompiling (Phase 0)
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/fingerprint.ps1 app.apk

# Decompile
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.ps1 app.apk
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.ps1 -Engine both -Deobf app.apk

# Find API calls
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.ps1 output/sources/
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.ps1 output/sources/ -Ktor -Apollo -Paths

# Kotlin name recovery
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/recover-kotlin-names.ps1 output/sources output/names
& plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.ps1 output/names LoginRepository

Kotlin name recovery (R8 deobfuscation)

Most real-world Kotlin/KMP apps ship through R8, so the decompiled classes come out as a.b.c. R8 renames the JVM symbols but cannot strip the Kotlin metadata strings; the Kotlin runtime (reflection, coroutines) needs the original fully-qualified names at runtime. This skill mines those @DebugMetadata / @Metadata annotations to rebuild an obfuscated → real class-name map. On a typical app it recovers ~100 % of the *Repository / *ViewModel / *UseCase / *Impl classes you actually want to read.

# 1. Build the mapping from the decompiled sources
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/recover-kotlin-names.sh output/sources/ output/names/
#    → output/names/mapping.tsv, mapping.json, by_package/

# 2. Query it: resolve an obfuscated name, search by real name, or grep
#    the sources with each hit annotated with its recovered class name
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ LoginRepository
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ -o a.b.c
bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ --grep 'login' output/sources/

Repository Structure

android-reverse-engineering-skill/
├── .claude-plugin/
│   └── marketplace.json                    # Marketplace catalog
├── plugins/
│   └── android-reverse-engineering/
│       ├── .claude-plugin/
│       │   └── plugin.json                 # Plugin manifest
│       ├── skills/
│       │   └── android-reverse-engineering/
│       │       ├── SKILL.md                # Core workflow (Phase 0–5)
│       │       ├── references/
│       │       │   ├── setup-guide.md
│       │       │   ├── jadx-usage.md
│       │       │   ├── fernflower-usage.md
│       │       │   ├── api-extraction-patterns.md
│       │       │   ├── kotlin-name-recovery.md
│       │       │   ├── third_party_hosts.txt   # denylist for first/third-party bucketing
│       │       │   └── call-flow-analysis.md
│       │       └── scripts/
│       │           ├── check-deps.sh       # Bash
│       │           ├── check-deps.ps1      # PowerShell
│       │           ├── install-dep.sh
│       │           ├── install-dep.ps1
│       │           ├── decompile.sh
│       │           ├── decompile.ps1
│       │           ├── fingerprint.sh          # Phase 0: pre-decompile triage
│       │           ├── fingerprint.ps1
│       │           ├── recover-kotlin-names.sh # R8 → real Kotlin class names
│       │           ├── recover-kotlin-names.ps1
│       │           ├── recover_kotlin_names.py
│       │           ├── lookup-name.sh          # query the recovered name map
│       │           ├── lookup-name.ps1
│       │           ├── lookup_names.py
│       │           ├── find-api-calls.sh
│       │           └── find-api-calls.ps1
│       └── commands/
│           └── decompile.md                # /decompile slash command
├── .cursor/
│   └── skills/
│       └── android-reverse-engineering/
│           └── SKILL.md                    # Cursor project skill (thin wrapper)
├── LICENSE
└── README.md

References

• jadx: Dex to Java decompiler
• Fernflower: JetBrains analytical decompiler
• Vineflower: Fernflower community fork
• dex2jar: DEX to JAR converter
• apktool: Android resource decoder

Acknowledgments

Thanks to the contributors who have shaped this skill:

• @tajchert: Phase 0 fingerprinting, R8-resistant Kotlin name recovery (recover-kotlin-names.sh, lookup-name.sh), and Ktor / Apollo / Koin / HMAC extraction patterns (#16)
• @philjn: Native Windows / PowerShell support (check-deps.ps1, install-dep.ps1, decompile.ps1, find-api-calls.ps1) and split/bundled APK detection in decompile.sh (#8)
• @txhno: Migration to the maintained ThexXTURBOXx/dex2jar fork (#12)
• @muqiao215: Decompile partial-success handling, Fernflower timeout safeguard, intermediate-artifact directory (#10)
• @kevinaimonster: Chinese localization (SKILL.md discovery keywords) (#4)

Disclaimer

This plugin is provided strictly for lawful purposes, including but not limited to:

• Security research and authorized penetration testing
• Interoperability analysis permitted under applicable law (e.g., EU Directive 2009/24/EC, US DMCA §1201(f))
• Malware analysis and incident response
• Educational use and CTF competitions

You are solely responsible for ensuring that your use of this tool complies with all applicable laws, regulations, and terms of service. Unauthorized reverse engineering of software you do not own or do not have permission to analyze may violate intellectual property laws and computer fraud statutes in your jurisdiction.

The authors disclaim any liability for misuse of this tool.

License

Apache 2.0; see LICENSE