230 lines
12 KiB
Markdown
230 lines
12 KiB
Markdown
# Android Reverse Engineering & API Extraction — Claude Code skill
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[](https://opensource.org/licenses/Apache-2.0) [](https://github.com/SimoneAvogadro/android-reverse-engineering-skill/stargazers) [](https://github.com/SimoneAvogadro/android-reverse-engineering-skill/commits/master)
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A Claude Code skill 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.
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> **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](#kotlin-name-recovery-r8-deobfuscation) below.
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> **Windows / PowerShell support (experimental)**: The `*.ps1` scripts alongside the bash ones are a recent community contribution, still being stabilised. For any issues please open an issue on **this** repository (not on the contributors' upstream forks): the PowerShell scripts are maintained here by [@SimoneAvogadro](https://github.com/SimoneAvogadro).
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## Table of Contents
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- [What it does](#what-it-does)
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- [Requirements](#requirements)
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- [Installation](#installation)
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- [Usage](#usage)
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- [Repository Structure](#repository-structure)
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- [References](#references)
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- [Acknowledgments](#acknowledgments)
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- [Disclaimer](#disclaimer)
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- [License](#license)
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## What it does
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| Capability | Description |
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|------------|-------------|
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| **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 |
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| **Decompile** | APK, XAPK, JAR, and AAR files using jadx and Fernflower/Vineflower (single engine or side-by-side comparison) |
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| **Recover Kotlin names** | Rebuild original `*Repository` / `*ViewModel` / `*UseCase` class names from R8-obfuscated binaries using Kotlin metadata that R8 cannot strip |
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| **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 |
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| **Trace call flows** | From Activities/Fragments through ViewModels and repositories down to HTTP calls |
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| **Analyze structure** | Manifest, packages, architecture patterns |
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| **Handle obfuscation** | R8-resistant path/URL extraction plus strategies for navigating ProGuard/R8 output |
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## Requirements
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**Required:**
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- Java JDK 17+
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- [jadx](https://github.com/skylot/jadx) (CLI)
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**Optional (recommended):**
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- [Vineflower](https://github.com/Vineflower/vineflower) or [Fernflower](https://github.com/JetBrains/fernflower) — better output on complex Java code
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- [dex2jar](https://github.com/ThexXTURBOXx/dex2jar) — needed to use Fernflower on APK/DEX files
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See `plugins/android-reverse-engineering/skills/android-reverse-engineering/references/setup-guide.md` for detailed installation instructions.
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## Installation
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### From GitHub (recommended)
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Inside Claude Code, run:
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```text
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/plugin marketplace add SimoneAvogadro/android-reverse-engineering-skill
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/plugin install android-reverse-engineering@android-reverse-engineering-skill
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```
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The skill will be permanently available in all future sessions.
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### From a local clone
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```bash
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git clone https://github.com/SimoneAvogadro/android-reverse-engineering-skill.git
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```
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Then in Claude Code:
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```text
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/plugin marketplace add /path/to/android-reverse-engineering-skill
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/plugin install android-reverse-engineering@android-reverse-engineering-skill
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```
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## Usage
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### Slash command
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```text
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/decompile path/to/app.apk
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```
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This runs the full workflow: dependency check, decompilation, and initial structure analysis.
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### Natural language
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The skill activates on phrases like:
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- "Decompile this APK"
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- "Reverse engineer this Android app"
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- "Extract API endpoints from this app"
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- "Follow the call flow from LoginActivity"
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- "Analyze this AAR library"
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### Manual scripts
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The scripts can also be used standalone:
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```bash
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# Check dependencies
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/check-deps.sh
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# Install a missing dependency (auto-detects OS and package manager)
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/install-dep.sh jadx
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/install-dep.sh vineflower
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# Fingerprint an APK/XAPK BEFORE decompiling (Phase 0 triage):
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# framework, HTTP stack, obfuscation level, native libs, notable SDKs
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/fingerprint.sh app.apk
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# Decompile APK with jadx (default)
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh app.apk
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# Decompile XAPK (auto-extracts and decompiles each APK inside)
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh app-bundle.xapk
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# Decompile with Fernflower
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh --engine fernflower library.jar
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# Run both engines and compare
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/decompile.sh --engine both --deobf app.apk
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# Find API calls — defaults to a full scan across every supported stack
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --retrofit
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --urls
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# Modern Kotlin/KMP stacks and obfuscation-resistant extraction
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --ktor # Ktor client
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --apollo # Apollo / GraphQL
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/find-api-calls.sh output/sources/ --paths # quoted path literals that survive R8 inlining
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```
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### Kotlin name recovery (R8 deobfuscation)
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Most real-world Kotlin/KMP apps ship through R8, so the decompiled classes come
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out as `a.b.c`. R8 renames the JVM symbols but **cannot strip the Kotlin
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metadata strings** — the Kotlin runtime (reflection, coroutines) needs the
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original fully-qualified names at runtime. This skill mines those
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`@DebugMetadata` / `@Metadata` annotations to rebuild an `obfuscated → real`
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class-name map. On a typical app it recovers ~100 % of the
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`*Repository` / `*ViewModel` / `*UseCase` / `*Impl` classes you actually want to
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read.
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```bash
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# 1. Build the mapping from the decompiled sources
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/recover-kotlin-names.sh output/sources/ output/names/
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# → output/names/mapping.tsv, mapping.json, by_package/
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# 2. Query it: resolve an obfuscated name, search by real name, or grep
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# the sources with each hit annotated with its recovered class name
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ LoginRepository
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ -o a.b.c
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bash plugins/android-reverse-engineering/skills/android-reverse-engineering/scripts/lookup-name.sh output/names/ --grep 'login' output/sources/
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```
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## Repository Structure
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```text
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android-reverse-engineering-skill/
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├── .claude-plugin/
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│ └── marketplace.json # Marketplace catalog
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├── plugins/
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│ └── android-reverse-engineering/
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│ ├── .claude-plugin/
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│ │ └── plugin.json # Plugin manifest
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│ ├── skills/
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│ │ └── android-reverse-engineering/
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│ │ ├── SKILL.md # Core workflow (Phase 0–5)
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│ │ ├── references/
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│ │ │ ├── setup-guide.md
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│ │ │ ├── jadx-usage.md
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│ │ │ ├── fernflower-usage.md
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│ │ │ ├── api-extraction-patterns.md
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│ │ │ ├── kotlin-name-recovery.md
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│ │ │ ├── third_party_hosts.txt # denylist for first/third-party bucketing
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│ │ │ └── call-flow-analysis.md
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│ │ └── scripts/
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│ │ ├── check-deps.sh # Bash
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│ │ ├── check-deps.ps1 # PowerShell
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│ │ ├── install-dep.sh
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│ │ ├── install-dep.ps1
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│ │ ├── decompile.sh
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│ │ ├── decompile.ps1
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│ │ ├── fingerprint.sh # Phase 0 — pre-decompile triage
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│ │ ├── recover-kotlin-names.sh # R8 → real Kotlin class names
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│ │ ├── lookup-name.sh # query the recovered name map
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│ │ ├── find-api-calls.sh
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│ │ └── find-api-calls.ps1
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│ └── commands/
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│ └── decompile.md # /decompile slash command
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├── LICENSE
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└── README.md
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```
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## References
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- [jadx — Dex to Java decompiler](https://github.com/skylot/jadx)
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- [Fernflower — JetBrains analytical decompiler](https://github.com/JetBrains/fernflower)
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- [Vineflower — Fernflower community fork](https://github.com/Vineflower/vineflower)
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- [dex2jar — DEX to JAR converter](https://github.com/ThexXTURBOXx/dex2jar)
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- [apktool — Android resource decoder](https://apktool.org/)
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## Acknowledgments
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Thanks to the contributors who have shaped this skill:
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- [@tajchert](https://github.com/tajchert) — Phase 0 fingerprinting, R8-resistant Kotlin name recovery (`recover-kotlin-names.sh`, `lookup-name.sh`), and Ktor / Apollo / Koin / HMAC extraction patterns (#16)
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- [@philjn](https://github.com/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)
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- [@txhno](https://github.com/txhno) — Migration to the maintained [`ThexXTURBOXx/dex2jar`](https://github.com/ThexXTURBOXx/dex2jar) fork (#12)
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- [@muqiao215](https://github.com/muqiao215) — Decompile partial-success handling, Fernflower timeout safeguard, intermediate-artifact directory (#10)
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- [@kevinaimonster](https://github.com/kevinaimonster) — Chinese localization (`SKILL.md` discovery keywords) (#4)
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## Disclaimer
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This plugin is provided strictly for **lawful purposes**, including but not limited to:
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- Security research and authorized penetration testing
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- Interoperability analysis permitted under applicable law (e.g., EU Directive 2009/24/EC, US DMCA §1201(f))
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- Malware analysis and incident response
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- Educational use and CTF competitions
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**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.
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The authors disclaim any liability for misuse of this tool.
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## License
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Apache 2.0 — see [LICENSE](LICENSE)
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