ClaudeSmalltalk

Interface for Claude to interact with live Smalltalk images (Cuis and Squeak) via MCP (Model Context Protocol).

This project enables Claude to evaluate Smalltalk code, browse classes, define methods, and more in a running Smalltalk environment.

Developed by John M McIntosh, Corporate Smalltalk Consulting Ltd. 2026

Four MCP Server Options

Option B: Cuis Native MCP (RECOMMENDED for Cuis)

┌─────────────┐     MCP/stdio     ┌─────────────────┐
│   Claude    │ ◄────────────────► │ Cuis Smalltalk  │
│  (Desktop   │    (JSON Lines)    │   (headless)    │
│  or Code)   │                    │   MCPServer     │
└─────────────┘                    └─────────────────┘

• Simplest setup - No Python, no MQTT broker required
• Claude spawns the Cuis image directly
• 12 tools available (saveImage intentionally excluded for safety)

Option C: Squeak Native MCP (RECOMMENDED for Squeak)

┌─────────────┐     MCP/stdio     ┌─────────────────┐
│   Claude    │ ◄────────────────► │ Squeak 6.0      │
│  (Desktop   │    (JSON Lines)    │   (with GUI)    │
│  or Code)   │                    │   MCPServer     │
└─────────────┘                    └─────────────────┘

• Responsive GUI - Squeak GUI remains responsive during MCP operations
• Uses OSProcess with BufferedAsyncFileReadStream for non-blocking stdio
• 12 tools available (same as Cuis)
• Server-side processing: 0-3ms per request

Option A: Python/MQTT Bridge

┌─────────────┐     MCP      ┌─────────────────┐     MQTT      ┌─────────────────┐
│   Claude    │ ◄──────────► │  claudeCuis_mcp │ ◄───────────► │ Cuis Smalltalk  │
│  (Desktop   │   (stdio)    │    (Python)     │  (pub/sub)    │     Image       │
│  or Code)   │              │                 │               │ ClaudeHandler   │
└─────────────┘              └─────────────────┘               └─────────────────┘

• Good for development (image stays running with GUI)
• Requires Python 3.10+ and MQTT broker

Option D: OpenAI Bridge (ChatGPT)

┌─────────────┐     HTTPS     ┌─────────────────┐    stdio/MCP    ┌─────────────────┐
│   OpenAI    │ ◄────────────► │  openai_mcp.py  │ ◄──────────────► │ Squeak 6.0      │
│   (Cloud)   │   (API calls)  │  (Python)       │   (JSON-RPC)    │   MCPServer     │
└─────────────┘                └─────────────────┘                 └─────────────────┘

• Enables ChatGPT to execute Smalltalk code via the same 12 tools
• Requires Python 3.10+ and OpenAI API key
• See OPENAI-SETUP.md for detailed instructions

Prerequisites

For Option B (Cuis Native MCP):

• Cuis Smalltalk VM (Squeak VM or Cog VM)
• ClaudeCuis.image (provided, or build your own)

For Option C (Squeak Native MCP):

• Squeak 6.0 from https://squeak.org/downloads/
• OSProcess package (installed via Monticello)
• See SQUEAK-SETUP.md for detailed instructions

For Option A (Python/MQTT Bridge):

• Python 3.10+ (MCP SDK requirement)
• MQTT Broker (e.g., Mosquitto) accessible from both Claude and the Smalltalk image
• Cuis Smalltalk image with Network-Kernel package

For Option D (OpenAI Bridge):

• Python 3.10+ (OpenAI SDK requirement)
• OpenAI API Key from https://platform.openai.com/api-keys
• Squeak 6.0 with MCP server (same as Option C)

Installation: Option B (Cuis Native MCP)

1. Configure Claude

For Claude Code (CLI)

Add to ~/.claude.json or project .claude.json:

{
  "mcpServers": {
    "cuisDirect": {
      "type": "stdio",
      "command": "/path/to/CuisVM.app/Contents/MacOS/Squeak",
      "args": ["/path/to/ClaudeCuis.image", "--mcp"]
    }
  }
}

For Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or equivalent:

{
  "mcpServers": {
    "cuisDirect": {
      "command": "/path/to/CuisVM.app/Contents/MacOS/Squeak",
      "args": ["/path/to/ClaudeCuis.image", "--mcp"]
    }
  }
}

2. (Optional) Build Your Own Image

If you want to build your own image instead of using the provided ClaudeCuis.image:

Feature require: 'JSON'.
CodePackageFile installPackage: '/path/to/MCP-Server.pck.st' asFileEntry.
Smalltalk saveImage.

The MCP server starts automatically when the image is launched with --mcp.

Installation: Option C (Squeak Native MCP)

See SQUEAK-SETUP.md for detailed step-by-step instructions.

Quick Start

1. Download Squeak 6.0 from https://squeak.org/downloads/
2. Install OSProcess via Monticello Browser (repository: http://www.squeaksource.com/OSProcess)
3. File in MCP-Server-Squeak.st
4. Register startup: Smalltalk addToStartUpList: MCPServer
5. Save image as ClaudeSqueak6.0.image
6. Configure Claude Code:

{
  "mcpServers": {
    "squeakDirect": {
      "type": "stdio",
      "command": "/path/to/Squeak6.0.app/Contents/MacOS/Squeak",
      "args": ["/path/to/ClaudeSqueak6.0.image", "--mcp"]
    }
  }
}

Note: The Squeak image is NOT provided in this repository. Users build their own from a fresh Squeak 6.0 download, ensuring they have the latest VM and can customize their environment.

Installation: Option A (Python/MQTT Bridge)

1. Set Up Python Environment

# Create virtual environment
python3 -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

# Install dependencies
pip install -r requirements.txt

2. Load Cuis Packages

Load the packages in this order in your Cuis Smalltalk image:

Feature require: 'Network-Kernel'.  "If not already loaded"

Then file in the packages:

1. MQTT-Cuis.pck.st - MQTT client library
2. ClaudeCuis.pck.st - Claude handler

Optional test packages:

• MQTT-Cuis-Tests.pck.st - MQTT unit tests
• MQTT-Cuis-IntegrationTests.pck.st - Integration tests
• ClaudeCuis-Tests.pck.st - Handler unit tests

3. Start ClaudeHandler in Cuis

| client handler |
client := MQTTClientInterface
    openOnHostName: 'your-mqtt-broker'
    port: 1883
    keepAlive: 60.
client username: 'your-username' password: 'your-password'.
client connect.
handler := ClaudeHandler on: client imageId: 'dev1'.
handler start.

4. Configure Claude

For Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or equivalent:

{
  "mcpServers": {
    "claudeCuis": {
      "command": "/path/to/venv/bin/python",
      "args": ["/path/to/claudeCuis_mcp.py"],
      "env": {
        "MQTT_BROKER": "your-mqtt-broker",
        "MQTT_PORT": "1883",
        "MQTT_USERNAME": "your-username",
        "MQTT_PASSWORD": "your-password",
        "CLAUDE_IMAGE_ID": "dev1",
        "CLAUDE_TIMEOUT": "30"
      }
    }
  }
}

For Claude Code (CLI)

Add to ~/.claude.json or project .claude.json:

{
  "mcpServers": {
    "claudeCuis": {
      "type": "stdio",
      "command": "/path/to/venv/bin/python",
      "args": ["/path/to/claudeCuis_mcp.py"],
      "env": {
        "MQTT_BROKER": "your-mqtt-broker",
        "MQTT_PORT": "1883",
        "MQTT_USERNAME": "your-username",
        "MQTT_PASSWORD": "your-password",
        "CLAUDE_IMAGE_ID": "dev1",
        "CLAUDE_TIMEOUT": "30"
      }
    }
  }
}

5. (Optional) Add Smalltalk Skill for Claude Code

Create .claude/skills/smalltalk/SKILL.md in your project:

mkdir -p .claude/skills/smalltalk
cp examples/SKILL.md .claude/skills/smalltalk/

This enables /smalltalk command and auto-invocation for Smalltalk tasks.

Installation: Option D (OpenAI Bridge)

See OPENAI-SETUP.md for detailed step-by-step instructions.

Quick Start

1. Set up Squeak MCP server (same as Option C)
2. Install Python dependencies:

python3 -m venv venv
source venv/bin/activate
pip install openai>=1.0.0

3. Set environment variables:

export OPENAI_API_KEY="sk-..."
export SQUEAK_VM_PATH="/path/to/Squeak"
export SQUEAK_IMAGE_PATH="/path/to/ClaudeSqueak.image"

4. Run the bridge:

# Interactive mode
python openai_mcp.py

# Single query mode
python openai_mcp.py "Evaluate 3 factorial in Smalltalk"

Available Tools

Usage Examples

Once configured, you can ask Claude:

• "Evaluate 3 factorial in Smalltalk"
• "Browse the OrderedCollection class"
• "Show me the source of String>>asUppercase"
• "What are the subclasses of Collection?"
• "Create a new class called Counter with an instance variable 'count'"

Environment Variables

MQTT Topics

• Requests: claude/request/{imageId} - JSON requests from Claude
• Responses: claude/response/{requestId} - JSON responses from Smalltalk

Testing

Test MQTT Connectivity

# Subscribe to all topics (verify broker access)
mosquitto_sub -h your-broker -u your-user -P 'your-pass' -t '#' -v

# In another terminal, test the Python bridge
export MQTT_BROKER=your-broker
export MQTT_USERNAME=your-user
export MQTT_PASSWORD=your-pass
python claudeCuis_mcp.py

Run Smalltalk Tests

"Unit tests (no broker needed)"
MQTTPacketTest buildSuite run inspect.
ClaudeHandlerTest buildSuite run inspect.

"Integration tests (requires running broker)"
MQTTIntegrationTest configureBroker: 'your-broker' port: 1883 username: 'user' password: 'pass'.
MQTTConnectionTest buildSuite run inspect.

Troubleshooting

MCP Server Won't Start

• Ensure Python 3.10+ is being used: python3 --version
• Verify the path to the venv Python is correct
• Check MCP dependencies: pip list | grep mcp

MQTT Connection Issues

• Test broker connectivity: mosquitto_sub -h broker -u user -P pass -t '#'
• Verify credentials and ACL permissions on the broker
• Check firewall allows port 1883

No Response from Smalltalk

• Ensure ClaudeHandler is started in Cuis
• Verify the imageId matches between config and handler
• Check MQTT subscription topics have proper ACL access

Squeak GUI Freezes (Option C)

• Verify OSProcess is installed: OSProcess thisOSProcess should return a UnixProcess
• Check that BufferedAsyncFileReadStream is being used by MCPTransport
• See SQUEAK-SETUP.md for troubleshooting details

Files

License

MIT License