nREPL MCP
Enables interaction with a running Clojure nREPL instance for evaluating Clojure code, inspecting namespaces, and retrieving connection statuses, compatible with MCP clients like Claude Desktop and CLine in VSCode.
What is nREPL MCP?
nREPL MCP is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to enables interaction with a running clojure nrepl instance for evaluating clojure code, inspecting namespaces, and retrieving connection statuses, compatible with mcp clients like claude desktop and cl...
Enables interaction with a running Clojure nREPL instance for evaluating Clojure code, inspecting namespaces, and retrieving connection statuses, compatible with MCP clients like Claude Desktop and CLine in VSCode.
This server falls under the Developer Tools and Coding Agents categories on MCPgee, the world's largest MCP server directory with 33,000+ servers.
Features
- Enables interaction with a running Clojure nREPL instance fo
Use Cases
Maintainer
Works with
Installation
Manual Installation
npx nrepl-mcp-serverConfiguration
Configuration Details
claude_desktop_config.json
Performance
Response Metrics
Resource Usage
How to Set Up and Use nREPL MCP
The nREPL MCP Server connects AI assistants to a live running Clojure nREPL instance, enabling evaluation of Clojure expressions, namespace inspection, variable introspection, and connection status monitoring through the Model Context Protocol. It bridges MCP clients like Claude Desktop and CLine in VSCode directly into your running Clojure application, making it possible to interactively explore and debug Clojure programs without leaving the AI chat interface. It communicates over STDIO and requires a pre-running nREPL server to connect to.
Prerequisites
- Node.js 18 or later installed
- A running Clojure nREPL server (started via lein repl, clj -M:nrepl, or your build tool)
- The nREPL host and port (typically localhost:7888 or as shown in your REPL output)
- An MCP client such as Claude Desktop or CLine in VSCode
Start your Clojure nREPL server
Before connecting, ensure your Clojure project has a running nREPL server. Note the host and port it starts on.
# With Leiningen:
lein repl
# With Clojure CLI tools:
clj -M:nreplAdd the server to your MCP client config
Add the nrepl-mcp-server entry to your Claude Desktop or CLine MCP settings file. The server is launched automatically by the MCP client.
{
"mcpServers": {
"nrepl-mcp-server": {
"command": "npx",
"args": ["nrepl-mcp-server"],
"disabled": false,
"autoApprove": []
}
}
}Restart your MCP client
Restart Claude Desktop or reload CLine in VSCode so it picks up the new MCP server configuration.
Connect to the running nREPL instance
Ask Claude to connect to your nREPL server by providing the host and port. The server exposes a connect tool that establishes the REPL session.
Evaluate Clojure code and inspect namespaces
Once connected, you can ask Claude to evaluate expressions, list project namespaces, inspect public vars, or check connection status.
nREPL MCP Examples
Client configuration
Claude Desktop or CLine JSON config for the nREPL MCP server.
{
"mcpServers": {
"nrepl-mcp-server": {
"command": "npx",
"args": ["nrepl-mcp-server"],
"disabled": false,
"autoApprove": []
}
}
}Prompts to try
Example prompts once connected to a running Clojure nREPL session.
- "Connect to my nREPL server at localhost port 7888"
- "Evaluate (+ 1 2 3) in the default namespace"
- "List all namespaces in this Clojure project"
- "Inspect the public vars in the myapp.core namespace"
- "Evaluate (def x 42) and then show me the value of x"
- "What is the current nREPL connection status?"Troubleshooting nREPL MCP
Connection to nREPL fails with 'connection refused'
Ensure your Clojure nREPL server is running before asking Claude to connect. Verify the host and port match the output shown when you started lein repl or clj -M:nrepl.
npx nrepl-mcp-server command not found or fails to start
Ensure Node.js 18+ is installed and npx is available. If the package fails to download, try running npm install -g nrepl-mcp-server and using command: "nrepl-mcp-server" without npx.
Namespace listing returns empty or missing namespaces
The namespace listing uses clojure.tools.namespace; ensure your project has this dependency available in the nREPL classpath. Load your project namespaces first with (require 'myapp.core) before listing.
Frequently Asked Questions about nREPL MCP
What is nREPL MCP?
nREPL MCP is a Model Context Protocol (MCP) server that enables interaction with a running clojure nrepl instance for evaluating clojure code, inspecting namespaces, and retrieving connection statuses, compatible with mcp clients like claude desktop and cline in vscode. It connects AI assistants to external tools and data sources through a standardized interface.
How do I install nREPL MCP?
Follow the installation instructions on the nREPL MCP GitHub repository. Clone the repo, install dependencies, and add the server config to your AI client.
Which AI clients work with nREPL MCP?
nREPL MCP works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.
Is nREPL MCP free to use?
Yes, nREPL MCP is open source and available under the ISC License license. You can use it freely in both personal and commercial projects.
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Quick Config Preview
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