Fake Store API MCP Server

Instructions

Implementation Reference

• src/tools/carts.ts:50-76 (handler)

  The addCart function implements the core logic for the fakestore_add_cart tool: validates inputs (userId, date, products), checks each product's productId and quantity, then posts to the FakeStore API to simulate adding a cart.

  export async function addCart(args: {
    userId: number;
    date: string;
    products: CartProduct[];
  }): Promise<Cart> {
    const { userId, date, products } = args;
  
    validatePositiveInteger(userId, 'User ID');
    validateISODate(date, 'Date');
    validateNonEmptyArray<CartProduct>(products, 'Products');
  
    // Validate each product in the cart
    products.forEach((product, index) => {
      if (typeof product.productId !== 'number' || product.productId <= 0) {
        throw new Error(`Product ${index + 1}: productId must be a positive number`);
      }
      if (typeof product.quantity !== 'number' || product.quantity <= 0) {
        throw new Error(`Product ${index + 1}: quantity must be a positive number`);
      }
    });
  
    return post<Cart>('/carts', {
      userId,
      date,
      products,
    });
  }

• src/tools/carts.ts:166-201 (schema)

  Input schema definition for fakestore_add_cart tool within the cartTools array, specifying required properties: userId (number), date (ISO string), products (array of {productId, quantity}).

  {
    name: 'fakestore_add_cart',
    description: 'Add a new cart (simulation - does not persist)',
    inputSchema: {
      type: 'object',
      properties: {
        userId: {
          type: 'number',
          description: 'User ID who owns the cart',
        },
        date: {
          type: 'string',
          description: 'Cart date in ISO format (e.g., 2024-01-01)',
        },
        products: {
          type: 'array',
          description: 'Array of products in the cart',
          items: {
            type: 'object',
            properties: {
              productId: {
                type: 'number',
                description: 'Product ID',
              },
              quantity: {
                type: 'number',
                description: 'Product quantity',
              },
            },
            required: ['productId', 'quantity'],
          },
        },
      },
      required: ['userId', 'date', 'products'],
    },
  },

• src/index.ts:138-147 (registration)

  MCP server registration: In the CallToolRequestSchema handler, checks if name === 'fakestore_add_cart' and invokes addCart with cast arguments, returning JSON-stringified result.

  if (name === 'fakestore_add_cart') {
    const result = await addCart(args as {
      userId: number;
      date: string;
      products: Array<{ productId: number; quantity: number }>;
    });
    return {
      content: [{ type: 'text', text: JSON.stringify(result, null, 2) }],
    };
  }

• src/index.ts:42-42 (registration)

  Tool list registration: In ListToolsRequestSchema handler, includes cartTools (containing fakestore_add_cart schema) in the returned tools list.

  tools: [...productTools, ...cartTools, ...userTools],

• src/index.ts:19-19 (registration)

  Imports the addCart handler function and cartTools (with schema) from carts.ts into the main MCP server index.

  import { cartTools, getAllCarts, getCartById, getUserCarts, addCart, updateCart, deleteCart } from './tools/carts.js';