DECX - Decompiler + X

A JADX-based Decompiler + X - Designed for AI-assisted code analysis

Overview

DECX (Decompiler + X) is a smart code analysis platform built on the JADX decompiler, designed specifically for AI-assisted code analysis. The platform provides powerful Java code analysis capabilities to AI assistants through an HTTP API, MCP (Model Context Protocol), a standalone CLI, and workflow skills.

Installation

Prerequisites

• Java: JDK 17+
• Node.js: 22.5+ for the CLI
• JADX: v1.5.2+ with plugin support if you use the GUI plugin

CLI And AI Skills

For AI-assisted CLI work, install the CLI and server JAR, then download the DECX skills for your agent:

npm install -g @jygzyc/decx-cli
decx self install
decx self skills install --client opencode --client codex

The CLI checks for updates in the background on startup: the result is cached under DECX_HOME for 24 hours and the check never blocks or breaks the command you ran. When a newer release exists, a one-line hint on stderr points you to decx self update. Set DECX_NO_UPDATE_CHECK=1 to disable the check.

Windows spawnSync npm.cmd EINVAL during self update

CLI versions older than v4.0.1 started npm.cmd directly on Windows, which can return EINVAL with some Node.js versions. An affected CLI cannot bootstrap this fix through self update; update it once from PowerShell or CMD instead:

npm.cmd install -g @jygzyc/decx-cli@latest

Reopen the terminal and run decx --version to confirm v4.0.1 or newer before using decx self update again. If an older version is still selected, run where.exe decx to check for multiple DECX CLI installations on PATH.

Skills are downloaded to ~/.decx/skills (or $DECX_HOME/skills) and linked into the selected client directories:

The skills/ directory contains:

JADX Plugin

Install the plugin from the JADX GUI plugin manager, or install a plugin JAR manually:

jadx plugins --install-jar <path-to-jadx_decx_plugin.jar>

After installation, open an APK/JAR in JADX and enable DECX. The plugin exposes the DECX HTTP API and MCP tools for the currently opened JADX project.

Usage

CLI + Skills

For agent-driven analysis, use the CLI to create a session and let the installed skills drive the detailed workflow:

decx process open target.apk --name target
decx code classes --limit 50
decx code search-global "WebView" --limit 20
decx android exported-components
decx android deep-links
decx process close target
decx process close --port 25419

Typical skill sequence:

• decx-cli for exploration, evidence gathering, and routing
• decx-vulnhunt for focused vulnerability hunting (App or Framework track)
• decx-report for generating reports from finalized finding writeups
• decx-poc for turning one finalized finding writeup into a buildable PoC

Vulnerability hunting keeps notes and finalized finding writeups in the working directory. Downstream report and PoC skills consume those finding writeups.

Useful command groups:

Notes:

• Session-backed code and android commands support --page <n> and can target a session with -s, --session <name> or a port with --port <port>.
• decx code class-source supports --limit <n> to return at most N source lines.
• decx process open <file> passes standard jadx-cli flags through, enables --show-bad-code and --no-imports by default, and strips --deobf because DECX analysis requires original names. It also defaults --rename-flags to case,valid (dropping the printable token) so heavily obfuscated Unicode identifiers such as Ď锬볝觧 survive decompilation instead of being aliased to m0.
• decx process open <file> --script s1.jadx.kts --script s2.jadx.kts runs Jadx Kotlin scripts during decompilation; the server bundles the jadx-script-kotlin plugin, so top-level code runs at load and afterLoad blocks after classes load. Reuse is keyed on the target file plus the script set.
• decx android resources supports file-name filtering with --include and --no-regex.
• decx android device system-services and permission-info are adb-backed commands. They use --serial / --adb-path, not --port <port>.
• decx android framework run collects from the connected device, processes, packs, and opens the final framework JAR by default; process [oem] is for local framework dumps and can resolve OEM from .artifact.json or a connected device when omitted.

Plugin + MCP

Use the plugin when you want the AI assistant to work against the project already opened in JADX GUI. The MCP server is an in-process Kotlin SDK Streamable HTTP endpoint; it is disabled by default and can be auto-started with the plugin:

1. Open the target APK/JAR in JADX.
2. Enable the DECX plugin and confirm the server is available at http://127.0.0.1:25419.
3. (Optional) Toggle Auto-start MCP with DECX in the DECX panel to start the MCP server at http://127.0.0.1:25420/mcp (HTTP port + 1) whenever DECX starts.
4. Connect your MCP client to DECX and call health_check().
5. Use MCP tools for code search/source/xrefs, Android manifest/resources/components, framework service lookup, and JADX GUI selections.

All MCP tools support pagination with page where the returned content is large.

Plugin options (stored in ~/.decx/config.json):

• decx.port: DECX HTTP server port, default 25419
• decx.mcpAutoStart: true/false, default false — auto-start the MCP server with DECX
• decx.cache: disk or memory, default disk

Error Codes

DECX returns the same structured error format from plugin and standalone server modes:

Error Response Format:

{
  "ok": false,
  "error": {
    "code": "CLASS_NOT_FOUND",
    "message": "Class not found: com.example.Foo"
  }
}

Development

Project Structure

Core request path:

CLI / MCP / HTTP
  -> DecxServer / RouteHandler
  -> DecxApi / DecxApiImpl
  -> service/* and utils/*

Build

cd decx
./gradlew dist

cd ../decx-cli
npm install
npm run build
npm test

Contributing

1. Fork this repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a Pull Request

License

This project is licensed under GNU License - see the LICENSE file for details.

Credits

• skylot/jadx - The foundation of this project, a powerful JADX decompiler with plugin support
• zinja-coder/jadx-ai-mcp - Provided many ideas and inspiration, excellent practices for JADX MCP integration
• Kotlin MCP SDK: In-process MCP server implementation
• Ktor: Streamable HTTP transport for the MCP server
• Javalin: Lightweight web framework for the HTTP API

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