Pharo Smalltalk implementation of Anthropic's Model Context Protocol (MCP) server specification. Enables LLMs like Claude to interact with Pharo applications.
# Pharo MCP Server
[](https://opensource.org/licenses/MIT)
[](https://mcpreview.com/mcp-servers/paulwilke/pharo-mcp-server)
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**Pharo Smalltalk implementation of Anthropic's Model Context Protocol (MCP) server specification. Enables LLMs like Claude to interact with Pharo applications.**
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## Table of Contents
* [What is MCP?](#what-is-mcp)
* [Goal of this Project](#goal-of-this-project)
* [Features](#features)
* [Installation](#installation)
* [Basic Usage](#basic-usage)
* [Defining Tools](#defining-tools)
* [Configuration](#configuration)
* [Development & Contributing](#development--contributing)
* [License](#license)
## What is MCP?
The Model Context Protocol (MCP), developed by Anthropic, is a specification designed to standardize how Large Language Models (LLMs) interact with external tools and services. It defines mechanisms for:
1. **Discovery:** How an LLM finds out if a service supports MCP and gets basic information.
2. **Service Description:** How a service describes its available tools (functions), including their names, purposes, input parameters, and output formats.
3. **Invocation:** How an LLM securely calls a specific tool with the required arguments and receives the result.
The goal is to make LLM tool usage more reliable, secure, and standardized.
For more details, see the official [Model Context Protocol GitHub organization](https://github.com/modelcontextprotocol).
## Goal of this Project
This project aims to provide a robust and easy-to-use **server-side implementation of the MCP specification** specifically for the **Pharo Smalltalk** environment.
It allows developers to expose functionalities within their Pharo applications (like querying data, creating objects, triggering actions) as "tools" that MCP-compliant LLMs (such as Claude 3) can discover and invoke through the standardized protocol.
This bridges the gap between the dynamic Pharo environment and the capabilities of modern LLMs.
## Features
* **MCP Specification Compliance:** Implements the core server-side endpoints:
* Discovery (`/.well-known/model-context`)
* Service Description (`/mcp/description` - or configurable path)
* Invocation (`/mcp/invoke` - or configurable path)
* **Dynamic Tool Registration:** Provides a simple API to register Pharo methods or blocks as MCP tools.
* **Automatic Service Description:** Generates the MCP Service Description JSON based on the registered tools and their metadata (name, description, schemas).
* **Web Server Integration:** Built upon the [Teapot](https://github.com/pharo-web/teapot) micro web framework.
* **JSON Handling:** Uses [NeoJSON](https://github.com/svenvc/NeoJSON) for robust JSON parsing and generation.
* **Extensible:** Designed to be integrated into larger Pharo applications.
* **(Planned):** Input validation using JSON Schema definitions for tool parameters.
* **(Planned):** Integration helpers for common Pharo object models (e.g., using [Voyage](https://github.com/pharo-nosql/voyage)).
## Installation
This project is intended to be loaded using Metacello.
1. **Ensure Metacello is loaded** in your Pharo image (it usually is).
2. **Execute the following code** in a Pharo Workspace (adjust the repository URL and branch/tag if necessary):
```smalltalk
Metacello new
baseline: 'MCPFramework'; "<- Use the actual name of YOUR baseline class (without 'BaselineOf')"
repository: 'github://YOUR_USERNAME/pharo-mcp-server:main/'; "<- CHANGE THIS to your repo URL and branch/tag"
load.