dejared-mcp

A Model Context Protocol (MCP) server for exploring, analyzing, and decompiling Java JAR files. Designed for AI-powered development tools, dejared-mcp connects your IDE or CLI assistant to inspect package structures, search bytecode, and decompile classes using CFR, Vineflower, or Procyon.

Table of Contents

• Overview
• Prerequisites
• Quick Start
• Features
• Decompiler Engines
• Installation and Configuration
• Custom Java Path
• Server Configuration
• How It Works
• FAQ and Troubleshooting
• Contributing
• Third-Party Licenses
• License

Overview

dejared-mcp is a Java-based MCP server distributed as an npm package. It provides nine tools organized into three categories: discovery, hunting, and deep analysis. AI assistants use these tools to navigate JAR file structures, search for classes and string literals in bytecode, and decompile .class files back to readable Java source code.

The npm package acts as a thin wrapper that downloads and caches the server JAR on first run, then spawns it via java -jar using stdio transport.

Prerequisites

• Node.js 18 or later
• Java 17 or later (JRE is sufficient)

Quick Start

Add the following to your MCP client configuration:

{
  "mcpServers": {
    "dejared": {
      "command": "npx",
      "args": ["-y", "dejared-mcp"]
    }
  }
}

See Installation and Configuration for tool-specific instructions.

Features

Discovery

Browse and read JAR contents.

Hunting

Search inside JAR files.

Deep Analysis

Inspect metadata and decompile classes.

Decompiler Engines

dejared-mcp supports three decompiler engines. The engine can be specified per request via the dejared_decompile_class tool.

Installation and Configuration

The standard configuration below works with most MCP-compatible tools. Expand the relevant section for tool-specific instructions.

{
  "mcpServers": {
    "dejared": {
      "command": "npx",
      "args": ["-y", "dejared-mcp"]
    }
  }
}

"amp.mcpServers": {
  "dejared": {
    "command": "npx",
    "args": ["-y", "dejared-mcp"]
  }
}

amp mcp add dejared -- npx -y dejared-mcp

{
  "mcpServers": {
    "dejared": {
      "command": "npx",
      "args": ["-y", "dejared-mcp"]
    }
  }
}

claude mcp add dejared -- npx -y dejared-mcp

claude plugin marketplace add hqkh4nh/dejared-mcp
claude plugin install dejared@dejared-mcp-marketplace

codex mcp add dejared npx "-y dejared-mcp"

[mcp_servers.dejared]
command = "npx"
args = ["-y", "dejared-mcp"]

/mcp add

{
  "mcpServers": {
    "dejared": {
      "type": "local",
      "command": "npx",
      "args": ["-y", "dejared-mcp"],
      "tools": ["*"]
    }
  }
}

gemini mcp add dejared npx -y dejared-mcp

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "dejared": {
      "type": "local",
      "command": ["npx", "-y", "dejared-mcp"],
      "enabled": true
    }
  }
}

{
  "servers": {
    "dejared": {
      "command": "npx",
      "args": ["-y", "dejared-mcp"]
    }
  }
}

Custom Java Path

If Java is not in your system PATH, set the DEJARED_JAVA_PATH environment variable in your MCP config. This applies to all npx-based configurations:

{
  "mcpServers": {
    "dejared": {
      "command": "npx",
      "args": ["-y", "dejared-mcp"],
      "env": {
        "DEJARED_JAVA_PATH": "/path/to/java"
      }
    }
  }
}

Server Configuration

How It Works

The npm package is a thin Node.js wrapper. On first run it:

1. Checks the platform cache directory for a cached JAR matching the current version.
   • Linux: $XDG_CACHE_HOME/dejared-mcp (defaults to ~/.cache/dejared-mcp)
   • macOS: ~/Library/Caches/dejared-mcp
   • Windows: %LOCALAPPDATA%\dejared-mcp
2. Downloads the JAR from GitHub Releases if not cached.
3. Spawns java -jar with stdio inherited for MCP transport.

The server communicates over stdio using the Model Context Protocol.

FAQ and Troubleshooting

Q: Java is installed but the server cannot find it.

Set the DEJARED_JAVA_PATH environment variable in your MCP configuration. See Custom Java Path.

Q: The server fails to start with a permission error.

Ensure that the cached JAR file is readable. The cache location depends on your platform. See How It Works for the cache directory paths.

Q: Decompilation times out or returns an error.

Some classes are difficult to decompile. Try a different engine by specifying vineflower or procyon in the dejared_decompile_class tool. The default timeout is 30 seconds and can be adjusted via dejared.security.decompile-timeout-seconds.

Q: Which Java version do I need?

Java 17 or later. A JRE is sufficient; you do not need a full JDK.

Q: Can I run the server without Node.js?

Yes. Download the JAR from GitHub Releases and run it directly with java -jar. See the "Pure Java" section under Installation and Configuration.

Contributing

Contributions are welcome. Please follow these guidelines:

1. Fork the repository and create a feature branch from master.
2. Ensure your changes compile and pass existing tests.
3. Write clear commit messages describing the purpose of each change.
4. Open a pull request against master with a description of what the change does and why.

Project Structure

dejared-mcp/
├── bin/            # Node.js CLI entry point
├── lib/            # Node.js wrapper (JAR download and process management)
├── java-mcp/       # Java MCP server (Spring Boot, Gradle)
│   └── src/
├── skills/         # Claude Code plugin skills
├── package.json    # npm package manifest
└── server.json     # MCP Registry manifest

Building from Source

cd java-mcp
./gradlew build

Reporting Issues

Open an issue on GitHub Issues with steps to reproduce the problem, your Java version, and your Node.js version.

Third-Party Licenses

This project uses the following open-source libraries:

License

This project is licensed under the MIT License.