🕷️ joern-mcp

A production-ready Model Context Protocol (MCP) server that provides AI assistants with static code analysis capabilities using Joern's Code Property Graph (CPG) technology.

Overview

The Joern MCP Server enables AI coding assistants to perform sophisticated static code analysis by leveraging Joern's powerful CPG-based analysis in isolated Docker environments. It implements the Model Context Protocol standard, making it compatible with various AI assistants and development environments.

Features

Static Code Analysis: Deep code analysis using Joern's CPG technology
Multi-Language Support: C/C++, Java, JavaScript/TypeScript, Python, Go, Kotlin, Scala, C#
Isolated Execution: All analysis runs in secure Docker containers
Intelligent Caching: Efficient CPG caching with configurable TTL
GitHub Integration: Direct analysis of GitHub repositories
Production Ready: Comprehensive error handling, logging, and monitoring
MCP Compliance: Full Model Context Protocol implementation

Quick Start

Prerequisites

Python 3.8+
Docker
Git

Installation

Clone the repository:
git clone https://github.com/Lekssays/joern-mcp.git cd joern-mcp
Install dependencies:
pip install -r requirements.txt
Build Joern Docker image:
# Option 1: Use the build script (recommended) ./build.sh # Option 2: Build manually docker build -t joern:latest .

Running the Server

Validate setup first:

python validate.py

Basic usage:

python main.py

With configuration file:

python main.py config.yml

Using environment variables:

export JOERN_DOCKER_IMAGE=joern:latest export JOERN_CACHE_DIR=/tmp/joern_cache export GITHUB_TOKEN=your_token_here python main.py

Note: The joern:latest image is built locally using the included Dockerfile, not pulled from a registry.

Configuration

Create a config.yml file for custom configuration:

docker: image: "joern:latest" cpu_limit: "2" memory_limit: "4g" timeout: 300 network_mode: "none" cache: enabled: true max_size_gb: 10 ttl_hours: 24 directory: "/tmp/joern_cache" max_concurrent_analyses: 3 github_token: "your_github_token" # Optional, for private repos log_level: "INFO"

Environment Variables

Variable	Description	Default
`JOERN_DOCKER_IMAGE`	Joern Docker image	`joern:latest`
`JOERN_CPU_LIMIT`	CPU limit for containers	`2`
`JOERN_MEMORY_LIMIT`	Memory limit for containers	`4g`
`JOERN_TIMEOUT`	Container timeout (seconds)	`300`
`JOERN_CACHE_ENABLED`	Enable CPG caching	`true`
`JOERN_CACHE_SIZE_GB`	Cache size limit (GB)	`10`
`JOERN_CACHE_DIR`	Cache directory	`/tmp/joern_cache`
`GITHUB_TOKEN`	GitHub access token	-
`JOERN_LOG_LEVEL`	Logging level	`INFO`

Usage with AI Assistants

VS Code with GitHub Copilot

Add to VS Code settings.json:

{ "servers": { "joern-mcp": { "type": "stdio", "command": "python", "args": [ "/path/to/joern-mcp/main.py" ] } }, "inputs": [] }

Claude Desktop

Configure in Claude Desktop settings:

{ "mcp": { "servers": [{ "name": "joern-mcp", "command": ["python", "main.py"], "workingDirectory": "/path/to/joern-mcp" }] } }

Available Tools

Core Tools

load_project: Load code from GitHub URL or local path
generate_cpg: Generate Code Property Graph for analysis
run_query: Execute Joern queries against the CPG
list_projects: List all loaded projects
project_info: Get detailed project information
cleanup_project: Clean up project resources

Pre-built Queries

list_queries: Access security, quality, and metrics queries

Security Queries

SQL injection detection
XSS sink identification
Hardcoded secrets discovery
Unsafe deserialization patterns

Quality Queries

Complex methods detection
Long methods identification
Duplicate code analysis
Unused variables discovery

Metrics Queries

Total methods/classes/files count
Average cyclomatic complexity

Example Usage

Load and Analyze a Project

# Example MCP client interaction { "tool": "load_project", "arguments": { "source": "https://github.com/user/repo", "branch": "main" } } { "tool": "generate_cpg", "arguments": { "project_id": "abc12345" } } { "tool": "run_query", "arguments": { "project_id": "abc12345", "query": "cpg.method.filter(_.cyclomaticComplexity > 10)" } }

Common Queries

Find all functions:

cpg.method.l

Find function calls:

cpg.call.l

Security analysis:

cpg.call.name(".*exec.*").code

Complex methods:

cpg.method.filter(_.cyclomaticComplexity > 10)

Development

Project Structure

joern-mcp/ ├── src/ │ ├── __init__.py │ ├── server.py # Main server implementation │ ├── models.py # Data models and exceptions │ ├── utils.py # Utility functions │ └── config.py # Configuration management ├── tests/ │ ├── conftest.py # Test configuration │ ├── test_server.py # Server integration tests │ ├── test_models.py # Model unit tests │ └── test_utils.py # Utility function tests ├── examples/ │ └── sample.c # Sample code for testing ├── main.py # Entry point ├── test_client.py # Simple test client ├── validate.py # Setup validation script ├── requirements.txt # Dependencies ├── Dockerfile # Joern Docker image ├── build.sh # Docker build script └── README.md

Running Tests

Run all tests:

pytest

Run with coverage:

pytest --cov=src --cov-report=html

Run integration tests (requires Docker):

pytest -m integration

Run specific test file:

pytest tests/test_server.py

Code Quality

Format code:

black src/ tests/ isort src/ tests/

Lint code:

flake8 src/ tests/ mypy src/

Troubleshooting

Common Issues

Docker connection error:

Ensure Docker is running
Check Docker daemon accessibility
Verify user permissions for Docker socket

Image not found:

Build the Joern image: docker build -t joern:latest .
Check image name in configuration
Verify the build completed successfully: docker images | grep joern

Docker build issues:

Ensure Docker has sufficient disk space
Check internet connectivity for downloading Joern
Try building with more verbose output: docker build -t joern:latest . --progress=plain

Memory issues:

Increase Docker memory limit in config
Reduce concurrent analysis limit
Clear cache directory

Permission errors:

Check file/directory permissions
Ensure cache directory is writable
Verify Docker socket permissions

Logging

Enable debug logging for troubleshooting:

export JOERN_LOG_LEVEL=DEBUG python main.py

Contributing

Fork the repository
Create a feature branch: git checkout -b feature-name
Make changes and add tests
Run tests and linting: pytest && black . && flake8
Commit changes: git commit -am 'Add feature'
Push to branch: git push origin feature-name
Submit a pull request

Acknowledgments

Joern - Static analysis platform
Model Context Protocol - AI assistant integration standard

Joern MCP Server