Ruby Melbourne talk: speed-run on AI and MCP with Ruby

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Action Plan

1. Side Intro
	Prompt Engineering
		- temperature, top-P, top-K
	Retrieval-Augmented Generation (RAG)
2. ModelContextProtocol (MCP)
- live 'vibe' code an app and integrate with LLM client
- have some fun

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About me

class Friendlyantz
  def initialize
    @name = 'Anton'
    @title = 'Extreme Programmer', 'Software Stuntman'
    @hobbies = ['kitesurfing', 'skatebords', 'MTB']
  end
  
  def find_more = 'https://friendlyantz.me/'

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class Intro::PromptEngineering
	temperature
	top-K
	top-P
end

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Temperate (0…1)

• 0 - predictable, ‘dry’, sober
• 1 - most creative

Start with 0.2

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Top K(1…)

max count of words with the highest probabilities. Start with 30

- I.e. `topK = 5`
["wine" (30%), "vino" (25%), "VB" (20%), "vermouth" (15%), "vine" (10%)]

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Top P(0..1)

The model sorts all words by probability. It keeps adding words until their cumulative probability exceeds P. good start with 0.95

		(i.e. 0.9) -> 

["Wine" (20%), "Vino" (20%), "Vinho" (20%), "Wein" (20%), "GrapeJuice" (10%), ...]

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Note: Extreme values cancel each other out

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"Balanced / coherent results with a touch of creativity"
	- temperature of .2,
	- top-P of .95, 
	- top-K of 30 
"Especially creative results"
	- temperature of .9
	- top-P of .99
	- top-K of 40. 
"Less creative results"
	- temperature of .1
	- top-P of .9
	- top-K of 20.

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Retrieval-augmented generation (RAG)

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RAG / embeddings are not the final answer, other resources are available in real world

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Model Context Protocol (MCP)

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great explanation of MCP https://www.youtube.com/watch?v=FLpS7OfD5-s

https://github.com/yjacquin/fast-mcp

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Time for…

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Vibe coding!

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create a simple shopping app that lists some funny vibing products in valid JSON , include 5 example products. make it simple, no need in web server, sinatra, etc, just simple calss. just vibes class. name file `vibes.rb`

add shopping cart functionality that can take quantity

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require "json"

class Vibes
  def initialize
    @products = [
      {id: 1, name: "Dancing Cactus", price: 19.99, description: "A cactus that dances to your favorite tunes."},
      {id: 2, name: "Vibing Sloth Mug", price: 12.99, description: "A mug with a sloth that vibes with your coffee."},
      {id: 3, name: "Mood Ring Lamp", price: 29.99, description: "A lamp that changes colors based on your mood."},
      {id: 4, name: "Chill Llama Pillow", price: 24.99, description: "A pillow shaped like a llama for ultimate chill vibes."},
      {id: 5, name: "Groovy Disco Ball", price: 34.99, description: "A mini disco ball to bring the groove to your room."}
    ]
    @cart = []
  end

  def list_products
    JSON.pretty_generate({products: @products})
  end

  def add_to_cart(product_id, quantity)
    product = @products.find { |p| p[:id] == product_id }
    if product
      @cart << {product: product, quantity: quantity}
      "Added #{quantity} of '#{product[:name]}' to the cart."
    else
      "Product not found."
    end
  end

  def view_cart
    JSON.pretty_generate(@cart.map do |item|
      {
        name: item[:product][:name],
        quantity: item[:quantity],
        total_price: (item[:product][:price] * item[:quantity]).round(2)
      }
    end)
  end
end

VIBES = Vibes.new

require "fast_mcp"

server = FastMcp::Server.new(name: "my-ai-server", version: "1.0.0")

class VibeProducts < FastMcp::Tool
  description "List some funny vibing products"

  def call
    VIBES.list_products
  end
end
server.register_tool(VibeProducts)

class AddToCart < FastMcp::Tool
  description "Add a product to the cart"

  arguments do
    required(:product_id).filled(:integer).description("The ID of the product to add")
    required(:quantity).filled(:integer).description("The quantity of the product to add")
  end

  def call(product_id:, quantity:)
    VIBES.add_to_cart(product_id.to_i, quantity.to_i)
  end
end
server.register_tool(AddToCart)

class ViewCart < FastMcp::Tool
  description "View the current shopping cart"

  def call
    VIBES.view_cart
  end
end

server.register_tool(ViewCart)
server.start

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Claude Desktop agent claude_desktop_config.json

{
  "mcpServers": {
    "vibe-mcp": {
      "command": "/PATH/ruby/3.4.4/bin/ruby",
      "args": [
        "/PATH/mcp-vibe/vibes.rb"
      ]
    },
    "mp-challenge": {
      "command": "/PATH/ruby/3.4.4/bin/ruby",
      "args": [
        "/PATH/promotions/app/app.rb"
      ]
    }
  }
}

chat history https://claude.ai/share/69c174c5-40b1-4f24-9769-583541d71c95 — REFERENCES:

• Prompt engineering paper by google
• https://docs.anthropic.com/en/docs/mcp