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.

| Tool | Description | |------|-------------| | dejared_list_packages | List all packages with class counts | | dejared_list_classes | List classes in a specific package | | dejared_list_resources | List non-class resource files | | dejared_read_resource | Read text resources (YAML, XML, properties, JSON, and others) |

Hunting

Search inside JAR files.

| Tool | Description | |------|-------------| | dejared_search_class | Search classes by name | | dejared_search_string | Search string literals in bytecode (URLs, SQL, error messages) |

Deep Analysis

Inspect metadata and decompile classes.

| Tool | Description | |------|-------------| | dejared_get_metadata | Extract class metadata via ASM (fast, no decompilation) | | dejared_dump_package_metadata | Batch metadata extraction for entire packages | | dejared_decompile_class | Decompile .class files to Java source code |

Decompiler Engines

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

| Engine | Description | |--------|-------------| | CFR (default) | Reliable general-purpose decompiler | | Vineflower | Modern fork of FernFlower, handles newer Java features well | | Procyon | Alternative engine, can handle some edge cases better |

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"]
    }
  }
}

Add via the Amp VS Code extension settings screen or by updating your settings.json file:

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

Amp CLI:

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

Edit ~/.gemini/antigravity/mcp_config.json:

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

Or install through the MCP Store if available.

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

Or add it to your project's .mcp.json using the standard config above.

Plugin (Marketplace) installs both the MCP server and the /jar-analysis skill:

claude plugin marketplace add HuynhKhanh1402/dejared-mcp
claude plugin install dejared@dejared-mcp-marketplace

Edit the Claude Desktop config file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Add the standard config above and restart Claude Desktop.

Add the standard config above to your MCP settings file.

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

Or edit ~/.codex/config.toml:

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

Interactive:

/mcp add

Then fill in:

• Server Name: dejared
• Server Type: STDIO
• Command: npx -y dejared-mcp

Or edit ~/.copilot/mcp-config.json:

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

Create or edit .cursor/mcp.json in your project root (project-level) or ~/.cursor/mcp.json (global) using the standard config above.

gemini mcp add dejared npx -y dejared-mcp

Or edit ~/.gemini/settings.json (global) or .gemini/settings.json (project) using the standard config above.

Use /mcp in a Gemini CLI session to verify the server is connected.

Go to Advanced settings > Extensions > Add custom extension. Name to your liking, use type STDIO, and set the command to npx -y dejared-mcp.

Go to Settings > Tools > AI Assistant > Model Context Protocol (MCP).

Click + Add and configure:

• Name: dejared
• Transport: Stdio
• Command: npx
• Arguments: -y dejared-mcp

Create or edit .kiro/settings/mcp.json using the standard config above.

Edit ~/.config/opencode/opencode.json:

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

Open Qodo Gen chat panel in VS Code or IntelliJ > Connect more tools > + Add new MCP > Paste the standard config above > Save.

Create or edit .vscode/mcp.json in your project root:

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

After saving, click the Start button that appears in the MCP config file, then use Agent mode in Copilot Chat.

Open Windsurf settings, navigate to MCP servers, and add a new server using the command type with npx -y dejared-mcp. Or add the standard config under mcpServers in your settings.

If you prefer to run the server JAR directly without Node.js:

1. Download the latest JAR from GitHub Releases.

2. Run it:

   java -jar dejared-mcp-0.2.0.jar

3. Configure your MCP client to use the JAR directly instead of npx:

   {
     "mcpServers": {
       "dejared": {
         "command": "java",
         "args": ["-jar", "/path/to/dejared-mcp-0.2.0.jar"]
       }
     }
   }

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

| Property | Default | Description | |----------|---------|-------------| | dejared.cache.max-size | 500 | Max entries in the decompilation LRU cache | | dejared.security.max-resource-size | 5242880 | Max resource file size (bytes) | | dejared.security.decompile-timeout-seconds | 30 | Timeout per decompilation |

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:

| Library | License | |---------|---------| | Spring Boot | Apache 2.0 | | Spring AI | Apache 2.0 | | ASM | BSD 3-Clause | | CFR | MIT | | Vineflower | Apache 2.0 | | Procyon | Apache 2.0 |

License

This project is licensed under the MIT License.