MCP Rand

Instructions

Implementation Reference

• src/handlers/draw-cards.handler.ts:102-160 (handler)

  The main handler function that executes the draw_cards tool: parses arguments, manages deck state, shuffles and draws cards, returns JSON result.
  export const drawCardsHandler = async ( request: CallToolRequest ): Promise<CallToolResult> => { const args = request.params.arguments as { count: number; deckState?: string }; if (args.count <= 0) { throw new McpError( ErrorCode.InvalidParams, 'Must draw at least one card' ); } // Validate and process deck state if provided let availableCards: Card[]; if (args.deckState) { // Validate base64 format if (!/^[A-Za-z0-9+/]+=*$/.test(args.deckState)) { throw new McpError( ErrorCode.InvalidParams, 'Invalid deck state: must be base64 encoded' ); } availableCards = getAvailableCardsFromState(args.deckState); } else { availableCards = createDeck(); } if (args.count > availableCards.length) { throw new McpError( ErrorCode.InvalidParams, `Cannot draw ${args.count} cards from deck with ${availableCards.length} cards remaining` ); } // Shuffle the available cards const shuffledCards = shuffleArray(availableCards); // Draw the requested number of cards const drawnCards = shuffledCards.slice(0, args.count); // Calculate remaining cards and get their state const remainingCards = shuffledCards.slice(args.count); const newDeckState = getDeckStateFromCards(remainingCards); const result = { drawnCards, remainingCount: remainingCards.length, deckState: newDeckState }; return { content: [ { type: 'text', text: JSON.stringify(result, null, 2) } ] }; };
• src/handlers/draw-cards.handler.ts:11-28 (schema)

  Tool specification defining name, description, and input schema for the draw_cards tool.
  export const toolSpec = { name: 'draw_cards', description: 'Draw cards from a standard deck of playing cards', inputSchema: { type: 'object' as const, properties: { count: { type: 'number', description: 'Number of cards to draw', }, deckState: { type: 'string', description: 'Optional base64 encoded string representing the current deck state', } }, required: ['count'] } };
• src/index.ts:17-26 (registration)

  Registers all tool handlers including draw_cards with the HandlerRegistry in the main server setup.
  async function registerHandlers(registry: HandlerRegistry): Promise<void> { registry.register('tools/list', 'list', ListToolsHandler as Handler); registry.register('tools/call', 'generate_uuid', generateUuidHandler as Handler); registry.register('tools/call', 'generate_random_number', generateRandomNumberHandler as Handler); registry.register('tools/call', 'generate_gaussian', generateGaussianHandler as Handler); registry.register('tools/call', 'generate_string', generateStringHandler as Handler); registry.register('tools/call', 'generate_password', generatePasswordHandler as Handler); registry.register('tools/call', 'roll_dice', rollDiceHandler as Handler); registry.register('tools/call', 'draw_cards', drawCardsHandler as Handler); }
• src/handlers/draw-cards.handler.ts:33-41 (helper)

  Helper function to create a full standard deck of 52 cards.
  function createDeck(): Card[] { const deck: Card[] = []; for (const suit of SUITS) { for (const value of VALUES) { deck.push({ suit, value }); } } return deck; }
• src/handlers/draw-cards.handler.ts:43-50 (helper)

  Fisher-Yates shuffle implementation for randomizing the deck.
  function shuffleArray<T>(array: T[]): T[] { const shuffled = [...array]; for (let i = shuffled.length - 1; i > 0; i--) { const j = Math.floor(Math.random() * (i + 1)); [shuffled[i], shuffled[j]] = [shuffled[j], shuffled[i]]; } return shuffled; }