Basilisp nREPL MCP server for AI agents

This bridge connects Anthropic's Model Control Protocol (MCP) with Basilisp's nREPL server, enabling Claude Code to interact directly with a Basilisp REPL. The tool allows for code execution, documentation lookup, namespace exploration, and more, providing a seamless integration between Claude and Basilisp.

Installation Requirements

uv
basilisp (from the basilisp repository)

Setup Instructions

Start a Basilisp nREPL server:
```
basilisp nrepl-server --port 36915
```

Add the MCP bridge to Claude Code:

claude mcp add /home/a/subjective/snr/basilisp_mcp_bridge.py

Using the Bridge

Once connected, you can use the following tools with Claude:

Evaluate Code
```
eval_code(code)
```
Executes Basilisp code and returns syntax-highlighted results
Get Documentation
```
get_docs(symbol)
```
Retrieves documentation for a specified symbol
List Variables in a Namespace
```
find_namespace_vars(namespace)
```
Shows all variables available in the specified namespace
List All Namespaces
```
list_namespaces()
```
Displays all available namespaces in the environment
Check Connection
```
check_connection()
```
Verifies that the nREPL server connection is working

Python Interoperability

Basilisp offers Python interop with proper syntax:

;; Import a module
(import [math :as math])

;; Access an attribute
(. math -pi)  ;; or (.-pi math)

;; Call a method
(.sin math 0)

;; Create Python data structures
#py{"key" "value"}

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 "basilisp-nrepl" '{"command":"python","args":["-m","basilisp_mcp_bridge"]}'

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": {
        "basilisp-nrepl": {
            "command": "python",
            "args": [
                "-m",
                "basilisp_mcp_bridge"
            ]
        }
    }
}

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": {
        "basilisp-nrepl": {
            "command": "python",
            "args": [
                "-m",
                "basilisp_mcp_bridge"
            ]
        }
    }
}

3. Restart Claude Desktop for the changes to take effect