Modex Minimal MCP Example

A minimal Model Context Protocol (MCP) plugin for Claude, built with Modex. This repository demonstrates how to wrap two simple tools—hello and inc—in a standalone Clojure server and integrate it into the Claude desktop application.

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Table of Contents

1. Prerequisites
2. Project Structure
3. Building the Uberjar
4. Running the Server
5. Claude Desktop Configuration
6. Troubleshooting
7. License

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Prerequisites

• Java 11+: Required to run the generated JAR.
• Clojure CLI Tools: Used by the build.sh script to compile and package.
• Git: To fetch the Modex dependency from GitHub.

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Project Structure

├── build.sh                 # Script to assemble the uberjar
├── deps.edn                 # Clojure CLI dependencies configuration
└── src
    └── modex
        └── minimal
            └── core.clj     # Namespace: modex.minimal.core

• build.sh: Uses hf.depstar to produce target/minimal-mcp.jar with AOT compilation and proper manifest.
• deps.edn: Declares Clojure, Modex, and other dependencies (including the Git SHA for Modex).
• src/modex/minimal/core.clj: Defines two tools—hello and inc—and the -main entrypoint that starts the MCP server.

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Building the Uberjar

Make the build script executable and run it:

chmod +x build.sh
./build.sh

Upon success, you’ll have:

target/minimal-mcp.jar

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Running the Server

Start the MCP server from the generated JAR:

java -jar target/minimal-mcp.jar

The server will listen on stdin/stdout for JSON-RPC v2.0 requests (e.g., from Claude).

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Claude Desktop Configuration

To wire this plugin into Claude’s desktop app, edit your config.json and add:

{
  "mcpServers": {
    "minimal-mcp": {
      "command": "java",
      "args": ["-jar", "/absolute/path/to/target/minimal-mcp.jar"]
    }
  },
  "globalShortcut": ""
}

• Replace /absolute/path/to/target/minimal-mcp.jar with the actual path on your machine.
• Optionally set a globalShortcut for quick activation.

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Troubleshooting

• ClassNotFoundException: Ensure your src/modex/minimal/core.clj has:

  (ns modex.minimal.core
    (:gen-class)
    …)
  

  and that build.sh specifies :main-class modex.minimal.core.

• Git dependency errors: In deps.edn, pin Modex correctly:

  theronic/modex {:git/url "https://github.com/theronic/modex.git"
                  :sha     "<commit-sha>"}
  

• Missing manifest entry: Verify with:

  unzip -p target/minimal-mcp.jar META-INF/MANIFEST.MF
  

  You should see:

  Main-Class: modex.minimal.core
  

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License

This example is provided under the MIT License. Feel free to adapt and extend it to build your own MCP tools with Modex.