MCP-Defender

MCP Defender is a Node.js desktop service that sits in front of MCP traffic for AI apps, automatically proxying all MCP tool call requests and responses so they can be inspected by Defender's signatures. Once started, it continuously monitors traffic between your AI apps (like Cursor, Claude, VS Code, Windsurf) and MCP endpoints, checks the data against a signature set, and raises alerts or blocks suspicious tool calls according to your configuration. You can interact with Defender through its UI/CLI (as provided by the app) to review intercepted payloads, apply allow/block decisions, and customize signature rules. The tool aims to reduce risk by catching potentially harmful tool invocations before they reach the target application or external services. To use it, start the Defender server, ensure MCP clients are routed through the Defender proxy, and then rely on the built-in alerts and controls to manage tool calls in real time.

Prerequisites:

• Node.js and npm installed on your system (v14+ recommended)
• Git installed

Steps:

1. Clone the repository git clone https://github.com/MCP-Defender/MCP-Defender.git cd MCP-Defender

2. Install dependencies npm install

3. Build or prepare the server if needed (depending on project setup) npm run build (if available)

4. Run the Defender server npm start

5. Verify the server is running Open http://localhost:3000 (or the port you configured) to access the Defender UI or check the console for startup logs.

Tips and common issues:

• Ensure the PORT environment variable is not blocked by another service. Change PORT in the env section if needed.
• If Defender encounters signature update issues, check network access for signature feeds and ensure you have the latest version of MCP Defender.
• When integrating with MCP clients, route traffic through Defender's proxy as described in your deployment guide.
• If the app fails to start, review npm install logs for missing native dependencies and rebuild as needed.
• You can customize or expand the signature set to better fit your environment; refer to the signature documentation in the project for guidance.