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.

Any ZIP-based Java archive works: .jar, .war, .ear, .aar, and
Spring Boot fat-jars.

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 20 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

Most clients accept this standard config:

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

If your tool has a CLI, one line is enough:

claude mcp add dejared -- npx -y dejared-mcp     # Claude Code
codex mcp add dejared -- npx -y dejared-mcp      # Codex
amp mcp add dejared -- npx -y dejared-mcp        # Amp
gemini mcp add dejared npx -y dejared-mcp        # Gemini CLI

Where the config file lives

Drop the standard config into the file for your tool:

Tool	Location
Claude Desktop	%APPDATA%\Claude\claude_desktop_config.json (Windows) · ~/Library/Application Support/Claude/claude_desktop_config.json (macOS)
Claude Code	.mcp.json in the project root
Cursor	.cursor/mcp.json (project) · ~/.cursor/mcp.json (global)
Windsurf	MCP servers panel in settings, or mcpServers in your settings file
Cline	MCP settings file, via the extension's MCP Servers panel
Antigravity Editor	~/.gemini/antigravity/mcp_config.json
Kiro	.kiro/settings/mcp.json
Copilot CLI	~/.copilot/mcp-config.json, or run /mcp add
Gemini CLI	~/.gemini/settings.json (global) · .gemini/settings.json (project)
Goose	Advanced settings → Extensions → Add custom extension, type STDIO
JetBrains IDEs	Settings → Tools → AI Assistant → Model Context Protocol (MCP)
Qodo Gen	Chat panel → Connect more tools → + Add new MCP

A few setups need more than the standard config — expand those below.

Codex — TOML instead of JSON

codex mcp add dejared -- npx -y dejared-mcp
codex mcp list

The -- matters: everything after it is the server's launch command.

Or edit ~/.codex/config.toml (global) or .codex/config.toml (project):

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

# Only if Java is not on your PATH
[mcp_servers.dejared.env]
DEJARED_JAVA_PATH = "/path/to/java"

VS Code (GitHub Copilot) — uses servers, not mcpServers

Create or edit .vscode/mcp.json:

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

After saving, click Start above the server entry, then use Agent mode in Copilot Chat.

opencode — command is an array

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

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

Claude Code plugin — also installs the /jar-analysis skill

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

Pure Java (no Node.js required)

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-<version>.jar
   

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

   {
     "mcpServers": {
       "dejared": {
         "command": "java",
         "args": ["-jar", "/path/to/dejared-mcp-<version>.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.