rails-mcp-playground

ValterAndrei/rails-mcp-playground

3.3

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This document provides a structured summary of a Model Context Protocol (MCP) server implemented using Ruby on Rails.

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README

MCP with Ruby on Rails

This is an example project that demonstrates the implementation of the MCP (Model-Controller-Provider) protocol using Ruby on Rails. MCP allows language models (LLMs) to interact with external tools through a JSON-RPC interface.

🚀 How to run the project

  • Install dependencies in your VSCode

  • Start the Rails server:

bin/rails server -b 0.0.0.0 -p 3000
  • Start the Rails server with rdbg (for debugging):
bundle exec rdbg --open --port 12345 --host 0.0.0.0 --nonstop --command -- \
  bin/rails server -b 0.0.0.0 -p 3000
  • Run tests:
bin/rails test

🧩 MCP Basic Concepts

1️⃣ Server (MCP Server)

👉 It's the one that provides tools (tools) that an AI can use.

  • It exposes JSON-RPC endpoints via /mcp.
  • It describes its tools in the tools/list method.
  • It executes a tool when the client requests it via tools/call.

2️⃣ Client (MCP Client)

👉 It's the one that consumes those tools (tools).

  • It can be an AI (like ChatGPT, Claude, Llama, etc).
  • Or an intermediary agent (e.g., a Python or Ruby script that connects the LLM to your MCP Server).
  • The client performs:
    • tools/list → asks "what tools do you offer?"
    • tools/call → executes a tool with certain parameters

🔶 Visual Diagram

                   ┌────────────────────────┐
                   │         User           │
                   │  "Create a post..."    │
                   └──────────┬─────────────┘
                              │
                              ▼
                  ┌────────────────────────┐
                  │    LLM (Client)        │
                  │  Ex: ChatGPT / Claude  │
                  │  or local LLM (Ollama) │
                  └──────────┬─────────────┘
                             │
                             │ JSON-RPC (tools/list, tools/call)
                             ▼
           ┌──────────────────────────────────────────┐
           │         🚀 Rails App (MCP Server)        │
           │     Exposing endpoint: /mcp              │
           │------------------------------------------│
           │ Tools:                                   │
           │  - post-create-tool                      │
           │  - post-delete-tool                      │
           │  - post-index-tool                       │
           │  - post-show-tool                        │
           │  - post-update-tool                      │
           │------------------------------------------│
           │ Uses Rails models and logic:             │
           │  Post.create, Post.all, etc.             │
           └──────────────────────────────────────────┘
                             │
                             ▼
               ┌──────────────────────────────────┐
               │    Database (PG)                 │
               │  posts(id, title, description)   │
               └──────────────────────────────────┘