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"]
    }
  }
}

<details> <summary><strong>Amp</strong></summary>

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

</details>

<details> <summary><strong>Antigravity Editor</strong></summary>

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

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

Or install through the MCP Store if available.

</details>

<details> <summary><strong>Claude Code</strong></summary>

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

</details>

<details> <summary><strong>Claude Desktop</strong></summary>

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.

</details>

<details> <summary><strong>Cline</strong></summary>

Add the standard config above to your MCP settings file.

</details>

<details> <summary><strong>Codex</strong></summary>

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

Or edit ~/.codex/config.toml:

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

</details>

<details> <summary><strong>Copilot CLI</strong></summary>

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": ["*"]
    }
  }
}

</details>

<details> <summary><strong>Cursor</strong></summary>

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

</details>

<details> <summary><strong>Gemini CLI</strong></summary>

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.

</details>

<details> <summary><strong>Goose</strong></summary>

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

</details>

<details> <summary><strong>JetBrains IDEs</strong></summary>

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

Click + Add and configure:

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

</details>

<details> <summary><strong>Kiro</strong></summary>

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

</details>

<details> <summary><strong>opencode</strong></summary>

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

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

</details>

<details> <summary><strong>Qodo Gen</strong></summary>

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

</details>

<details> <summary><strong>VS Code (GitHub Copilot)</strong></summary>

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.

</details>

<details> <summary><strong>Windsurf</strong></summary>

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.

</details>

<details> <summary><strong>Pure Java (no Node.js required)</strong></summary>

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"]
       }
     }
   }
   

</details>

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.