MCP for Pharo

MCP is an in-image Model Context Protocol server for Pharo. It lets MCP clients inspect and change the running image through Pharo-aware tools for packages, classes, methods, tests, repositories, change history, debugging, and UI inspection.

MCP works through the Pharo ecosystem—compilation, refactorings, Renraku, SUnit, Iceberg, Metacello, Epicea, and Spec—rather than patching exported Tonel files as plain text.

Supported Versions

Pharo 10, 11, 12, 13, 14, and 15 are supported.

Protocol revisions 2025-03-26, 2025-06-18, 2025-11-25 and 2026-07-28 are supported, each answered in its own shape.

Install And Start

Load MCP in a supported image:

Metacello new
   baseline: 'MCP';
   repository: 'github://Evref-BL/MCP:main/src';
   onConflictUseIncoming;
   load.

The baseline groups are:

• Core: the server, its transport and schema machinery, and the catalog tools it dispatches through
• IDE: the image tools — classes, methods, packages, tests, critiques, repositories, change history, debugging
• UI: the world-menu server list
• Telemetry: the OpenTelemetry backend
• default: Core, IDE, UI and their tests

A project embedding the server and serving tools of its own loads Core alone, which leaves out the image tools and everything behind them. Loading its package is all its tools need: a tool that names itself is in the catalog. Building on MCP walks through a tool, a resource and a prompt of your own.

Start the Streamable HTTP server:

MCP startOnPort: 4000.

That answers the server already on 4000 when the image has one, so running it again after a restart is safe. MCP allServers lists what the image holds, and Library → MCP Servers in the world menu shows the same list.

Connect a local MCP client to http://127.0.0.1:4000. Client configuration formats differ; see Getting started for setup and first calls.

Documentation

• Documentation index
• Getting started
• Building on MCP
• Observability and UI
• Tool reference
• Developing MCP

Agent Templates

Install the guide, local references, workflow skills, and direct MCP configuration for an agent host into the current project:

npx @evref-bl/pharo-mcp install --host claude

Use --host codex or --host opencode for those hosts. The direct MCP configuration expects port 4000; update it when the image uses another port.

Node integrations that provide their own MCP transport can install only the guide, skills, references, and soft-loading instruction block:

import { installGuidance } from "@evref-bl/pharo-mcp";

installGuidance({ host: "codex", cwd: process.cwd() });

Contributing

Use Pharo 14 for normal development and preserve Pharo 10, 11, 12, 13 and 15 compatibility. Live behavior must be verified in an image; source inspection alone is not enough. Start with AGENTS.md and MCP verification.