Skip to content

03-tools-prompts-resources-and-schema-discipline.md

Latest commit

 

History

History
169 lines (121 loc) · 4.9 KB

03-tools-prompts-resources-and-schema-discipline.md

File metadata and controls

169 lines (121 loc) · 4.9 KB
layout default
title Chapter 3: Tools, Prompts, Resources, and Schema Discipline
nav_order 3
parent MCP Ruby SDK Tutorial

Chapter 3: Tools, Prompts, Resources, and Schema Discipline

Welcome to Chapter 3: Tools, Prompts, Resources, and Schema Discipline. In this part of MCP Ruby SDK Tutorial: Building MCP Servers and Clients in Ruby, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

This chapter focuses on modeling MCP primitives with predictable behavior and schema quality.

Learning Goals

  • design tool schemas that validate arguments and output shapes reliably
  • structure prompt and resource handlers for maintainable growth
  • use annotations and metadata consistently across primitives
  • avoid schema drift that breaks client interoperability

Primitive Implementation Checklist

  1. define explicit tool argument schemas and output contracts
  2. model prompt arguments with stable names and titles
  3. expose resource identifiers and templates with clear naming patterns
  4. test edge cases for empty, invalid, and over-broad input payloads

Source References

Summary

You now have a schema-first primitive strategy for Ruby MCP servers.

Next: Chapter 4: Notifications, Logging, and Observability

Depth Expansion Playbook

Source Code Walkthrough

dev.yml

The dev module in dev.yml handles a key part of this chapter's functionality:

name: mcp-ruby

type: ruby

up:
  - ruby
  - bundler

commands:
  console:
    desc: Open console with the gem loaded
    run: bin/console
  build:
    desc: Build the gem using rake build
    run: bin/rake build
  test:
    desc: Run tests
    syntax:
      argument: file
      optional: args...
    run:  |
      if [[ $# -eq 0 ]]; then
        bin/rake test
      else
        bin/rake -I test "$@"
      fi
  style:
    desc: Run rubocop
    aliases: [rubocop, lint]
    run: bin/rake rubocop

This module is important because it defines how MCP Ruby SDK Tutorial: Building MCP Servers and Clients in Ruby implements the patterns covered in this chapter.

examples/streamable_http_server.rb

The streamable_http_server module in examples/streamable_http_server.rb handles a key part of this chapter's functionality:

# frozen_string_literal: true

$LOAD_PATH.unshift(File.expand_path("../lib", __dir__))
require "mcp"
require "rack/cors"
require "rackup"
require "json"
require "logger"

# Create a logger for SSE-specific logging
sse_logger = Logger.new($stdout)
sse_logger.formatter = proc do |severity, datetime, _progname, msg|
  "[SSE] #{severity} #{datetime.strftime("%H:%M:%S.%L")} - #{msg}\n"
end

# Tool that returns a response that will be sent via SSE if a stream is active
class NotificationTool < MCP::Tool
  tool_name "notification_tool"
  description "Returns a notification message that will be sent via SSE if stream is active"
  input_schema(
    properties: {
      message: { type: "string", description: "Message to send via SSE" },
      delay: { type: "number", description: "Delay in seconds before returning (optional)" },
    },
    required: ["message"],
  )

  class << self
    attr_accessor :logger

    def call(message:, delay: 0)
      sleep(delay) if delay > 0

      logger&.info("Returning notification message: #{message}")

This module is important because it defines how MCP Ruby SDK Tutorial: Building MCP Servers and Clients in Ruby implements the patterns covered in this chapter.

.rubocop.yml

The .rubocop module in .rubocop.yml handles a key part of this chapter's functionality:

inherit_gem:
  rubocop-shopify: rubocop.yml

plugins:
  - rubocop-minitest
  - rubocop-rake

AllCops:
  TargetRubyVersion: 2.7

Gemspec/DevelopmentDependencies:
  Enabled: true

Lint/IncompatibleIoSelectWithFiberScheduler:
  Enabled: true

Minitest/LiteralAsActualArgument:
  Enabled: true

This module is important because it defines how MCP Ruby SDK Tutorial: Building MCP Servers and Clients in Ruby implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[dev]
    B[streamable_http_server]
    C[.rubocop]
    A --> B
    B --> C
Loading