Babashka MCP server

This MCP server allows you to interact with Babashka (a native Clojure interpreter for scripting) through the Model Context Protocol. It provides a standardized way to execute Babashka code and access command history through a simple interface.

Prerequisites

Install Babashka

Babashka can be installed in several ways:

macOS

brew install borkdude/brew/babashka

Linux

bash < <(curl -s https://raw.githubusercontent.com/babashka/babashka/master/install)

Windows

# Using scoop
scoop install babashka

For other installation methods, see the official Babashka installation guide.

Verify Installation

After installation, verify Babashka works:

# Check version
bb --version

# Try a simple expression
bb -e '(+ 1 2 3)'

# Run a script from string
bb -e '(defn hello [x] (str "Hello, " x "!")) (hello "World")'

# Use -i flag to process lines of input
ls | bb -i '(take 2 *input*)'

Installation

Install and build the MCP server with:

# Install dependencies
npm install

# Build the MCP server
npm run build

Configuration

The server can be configured through environment variables:

• BABASHKA_PATH: Path to the Babashka executable (default: "bb")

Using the MCP Server

Execute Tool

The primary way to interact with the server is through the execute tool, which runs Babashka code:

{
  name: "execute",
  arguments: {
    code: string;      // Babashka code to execute
    timeout?: number;  // Timeout in milliseconds (default: 30000)
  }
}

Example Usage

To execute a simple Babashka expression:

{
  name: "execute",
  arguments: {
    code: "(+ 1 2 3)",
    timeout: 5000
  }
}

Accessing Command History

The server maintains a cache of recent command executions, which you can access through:

• babashka://commands/{index} - Access specific command results by index

Babashka Language Tips

Tail Call Optimization

When writing recursive functions in Babashka, use the recur special form to avoid stack overflow:

;; Recommended approach with TCO using recur
(defn countdown [n]
  (if (zero? n)
    :done
    (recur (dec n))))

Useful Resources

• Babashka Book - Official documentation
• Babashka Examples - Collection of example scripts
• Babashka GitHub Repository - The main Babashka project

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 "babashka" '{"command":"npx","args":["-y","babashka-mcp-server"]}'

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": {
        "babashka": {
            "command": "npx",
            "args": [
                "-y",
                "babashka-mcp-server"
            ]
        }
    }
}

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": {
        "babashka": {
            "command": "npx",
            "args": [
                "-y",
                "babashka-mcp-server"
            ]
        }
    }
}

3. Restart Claude Desktop for the changes to take effect