JetBrains IDE WebSocket Monitor MCP server

The MCP Proxy Sidecar extends JetBrains' MCP Server with WebSocket monitoring capabilities, allowing you to observe all Model Context Protocol interactions between clients (like Claude Desktop) and JetBrains IDEs in real-time.

Installation

Install the MCP Server Plugin

First, install the MCP Server Plugin for your JetBrains IDE: https://plugins.jetbrains.com/plugin/26071-mcp-server

Configure Claude Desktop

To use MCP Proxy Sidecar with Claude Desktop, you need to modify your Claude Desktop configuration file:

• MacOS: ~/Library/Application\ Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%/Claude/claude_desktop_config.json

Add the following configuration:

{
  "mcpServers": {
    "ide": {
      "command": "npx",
      "args": ["-y", "mcp-proxy-sidecar"],
      "env": {
        "WS_PORT": "27042"  // Optional: customize WebSocket port
      }
    }
  }
}

Configuration Options

You can customize the sidecar's behavior using environment variables in your Claude Desktop configuration:

Variable	Description	Default
WS_PORT	Port for WebSocket server	27042
IDE_PORT	Specific port for IDE connection	Auto-scans 63342-63352
HOST	Host address for IDE connection	127.0.0.1
LOG_ENABLED	Enable debug logging	false

Example with all configuration options:

{
  "mcpServers": {
    "ide": {
      "command": "npx",
      "args": ["-y", "mcp-proxy-sidecar"],
      "env": {
        "WS_PORT": "27042",
        "IDE_PORT": "63342",
        "HOST": "127.0.0.1",
        "LOG_ENABLED": "true"
      }
    }
  }
}

WebSocket Monitoring

The sidecar broadcasts all MCP tool calls as WebSocket notifications that you can monitor with any WebSocket client.

WebSocket Details

• Default port: 27042 (configurable via WS_PORT environment variable)
• Message format: JSON objects with the following structure:

interface MCPNotification {
  type: 'mcp-notification';
  payload: {
    endpoint: string;     // Tool name that was called
    content: any;         // Call arguments
    timestamp: string;    // ISO timestamp
  }
}

Architecture

The MCP Proxy Sidecar sits between your MCP client (like Claude Desktop) and the JetBrains IDE:

1. MCP clients communicate with the sidecar using the MCP protocol
2. The sidecar forwards commands to the JetBrains IDE
3. IDE responses are sent back through the sidecar to the client
4. All tool calls are broadcasted via WebSocket for monitoring

This architecture allows for seamless monitoring without affecting the normal operation of MCP clients and the IDE.

How to install this MCP server

For Claude Code

To add this MCP server to Claude Code, run this command in your terminal:

claude mcp add-json "ide" '{"command":"npx","args":["-y","mcp-proxy-sidecar"],"env":{"WS_PORT":"27042"}}'

See the official Claude Code MCP documentation for more details.

For Cursor

There are two ways to add an MCP server to Cursor. The most common way is to add the server globally in the ~/.cursor/mcp.json file so that it is available in all of your projects.

If you only need the server in a single project, you can add it to the project instead by creating or adding it to the .cursor/mcp.json file.

Adding an MCP server to Cursor globally

To add a global MCP server go to Cursor Settings > Tools & Integrations and click "New MCP Server".

When you click that button the ~/.cursor/mcp.json file will be opened and you can add your server like this:

{
    "mcpServers": {
        "ide": {
            "command": "npx",
            "args": [
                "-y",
                "mcp-proxy-sidecar"
            ],
            "env": {
                "WS_PORT": "27042"
            }
        }
    }
}

Adding an MCP server to a project

To add an MCP server to a project you can create a new .cursor/mcp.json file or add it to the existing one. This will look exactly the same as the global MCP server example above.

How to use the MCP server

Once the server is installed, you might need to head back to Settings > MCP and click the refresh button.

The Cursor agent will then be able to see the available tools the added MCP server has available and will call them when it needs to.

You can also explicitly ask the agent to use the tool by mentioning the tool name and describing what the function does.

For Claude Desktop

To add this MCP server to Claude Desktop:

1. Find your configuration file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json
• Linux: ~/.config/Claude/claude_desktop_config.json

2. Add this to your configuration file:

{
    "mcpServers": {
        "ide": {
            "command": "npx",
            "args": [
                "-y",
                "mcp-proxy-sidecar"
            ],
            "env": {
                "WS_PORT": "27042"
            }
        }
    }
}

3. Restart Claude Desktop for the changes to take effect