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.

Related MCP server: Vibe Coder MCP

Environment Requirements

• Python >= 3.10 (default 3.12) & uv

• Joern

Installation Steps

1. Clone the project locally:

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

2. 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

1. 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

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

3. 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

4. Configure MCP server Configure the mcp server in cline, refer to sample_cline_mcp_settings.json.

5. 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

Contribution Guidelines

Welcome to submit Issues and Pull Requests to help improve the project.

Welcome to add more tools.

References

https://github.com/flankerhqd/jebmcp

https://docs.joern.io/server/

https://docs.joern.io/interpreter/