idachev/mcp-javadc

A Model Context Protocol (MCP) server for decompiling Java class files. This server allows AI assistants and tools that implement the MCP protocol to decompile Java bytecode into readable source code.
Features
- Decompile Java .class files from file path
- Decompile Java classes from package name (e.g., java.util.ArrayList)
- Decompile Java classes from JAR files
- Specify which class to extract from JAR files
- Full MCP-compatible API
- Stdio transport for seamless integration
- Clean error handling
- Temporary file management
Prerequisites
- Node.js 16+
- npm
- No Java requirement (using JavaScript port of CFR decompiler)
Installation
Option 1: Using npx (Recommended)
You can run the server directly with npx without installing:
Option 2: Global Installation
Option 3: From Source
Usage
Quick Start
The easiest way to run the server:
Integrating with MCP Clients
To use with an MCP client (like Claude or another MCP-compatible AI assistant):
Adding to Claude Code
To add this tool to Claude Code:
Example MCP client configuration:
MCP Tools
The server provides three main tools:
1. decompile-from-path
Decompiles a Java .class file from a file path.
Parameters:
- classFilePath: Absolute path to the Java .class file
Example request:
2. decompile-from-package
Decompiles a Java class from a package name.
Parameters:
- packageName: Fully qualified Java package and class name (e.g., java.util.ArrayList)
- classpath: (Optional) Array of classpath directories to search
Example request:
3. decompile-from-jar
Decompiles a Java class from a JAR file.
Parameters:
- jarFilePath: Absolute path to the JAR file (required)
- className: Fully qualified class name to extract from the JAR (required) (e.g., "com.example.MyClass")
Example request:
Known Issues
Java Class Decompilation
The CFR decompiler (@run-slicer/cfr) is a JavaScript port of the popular CFR Java decompiler. It works well with:
1. Standard Java class files
2. Classes that are part of a known package structure
3. Modern Java features (all Java versions)
4. JAR files containing Java classes
If you encounter issues with a specific class file, try:
- Using the decompile-from-package tool with explicit classpath
- Using the decompile-from-jar tool with explicit class name
- Ensuring the class file is a valid Java bytecode file
- Checking for corrupt class files or JAR archives
Maven Repository Usage
When working with JAR files from Maven repositories:
- Use the find ~/.m2 -name "*dependency-name*jar" command to locate JAR files
- Filter out source and javadoc JARs using grep -v source | grep -v javadoc
- Use jar tf your-jar-file.jar | grep .class to list available classes in a JAR
- Check that class names match the package structure in the JAR
Configuration
Environment Variables
- CLASSPATH: Java classpath for finding class files (used when no classpath is specified)
Development
Testing with MCP Inspector