Joern MCP Server

A simple MCP Server for Joern.

Project Introduction

This project is an MCP Server based on Joern, providing a series of features to help developers with code review and security analysis.

Environment Requirements

Python >= 3.10 (default 3.12) & uv
Joern

Installation Steps

Clone the project locally:

git clone https://github.com/sfncat/mcp-joern.git
cd mcp-joern

Install Python dependencies:

uv venv .venv
source .venv/bin/activate
uv sync

Project Structure

├── server.py                       # MCP Server main program
├── test_mcp_client.py              # Test program for joern server and mcp tool
├── test_sc_tools.py                # Direct test program for sc tools
├── common_tools.py                 # Common utility functions
├── server_tools.py                 # Server utility functions
├── server_tools.sc                 # Scala implementation of server utility functions
├── server_tools_source.sc          # Scala implementation of server utility functions,use sourceCode to get the source code of method
├── requirements.txt                # Python dependency file
├── sample_cline_mcp_settings.json  # Sample cline mcp configuration file
└── env_example.txt                 # Environment variables example file

Usage

Start the Joern server:

joern -J-Xmx40G --server --server-host 127.0.0.1 --server-port 16162 --server-auth-username user --server-auth-password password --import server_tools.sc
Or
joern -J-Xmx40G --server --server-host 127.0.0.1 --server-port 16162 --server-auth-username user --server-auth-password password --import server_tools_source.sc

If you are using it under Windows, you may need to set the JVM system variables through the command line or in the system environment variables.

set _JAVA_OPTIONS=-Dfile.encoding=UTF-8

set joern logging level to ERROR

set SL_LOGGING_LEVEL=ERROR //windows
export SL_LOGGING_LEVEL=ERROR //linux

if you have the following warning

Unable to create a system terminal, creating a dumb terminal (enable debug logging for more information)

you can disable it by setting the environment variable

set TERM=dumb
export TERM=dumb

to restore the default behavior

set TERM=xterm-256color
export TERM=xterm-256color

Copy env_example.txt to .env Modify the configuration information to match the joern server startup configuration

Run the test connection: Modify the information in test_mcp_client.py to confirm the joern server is working properly

uv run test_mcp_client.py
Starting MCP server test...
==================================================
Testing server connection...
[04/16/25 20:38:54] INFO     Processing request of type CallToolRequest                                                                                                                     server.py:534
Connection test result: Successfully connected to Joern MCP, joern server version is XXX

Configure MCP server Configure the mcp server in cline, refer to sample_cline_mcp_settings.json.
Use MCP server Ask questions to the large language model, refer to prompts_en.md

Development Notes

.env file is used to store environment variables
.gitignore file defines files to be ignored by Git version control
pyproject.toml defines the Python configuration for the project
MCP tool development
- Implement in server_tools.sc, add definitions in server_tools.py, and add tests in test_mcp_client.py