Product Data and Transports

5.1 Product Data Structure

UCP uses JSON to describe products. All monetary amounts follow ISO 4217 minor currency units:

{
  "product": {
    "id": "prod_abc123",
    "name": "Classic Canvas Sneakers",
    "description": "Comfortable, breathable canvas shoes for everyday wear",
    "brand": "ExampleBrand",
    "category": "Shoes > Sneakers > Canvas",
    "sku": "SHOE-001",
    "gtin": "1234567890123",
    "url": "https://store.example.com/product/shoe-001",
    "images": [
      { "url": "https://store.example.com/images/shoe-1.jpg", "alt": "Front view", "width": 800, "height": 800 },
      { "url": "https://store.example.com/images/shoe-2.jpg", "alt": "Side view", "width": 800, "height": 800 }
    ],
    "price": {
      "amount": 5900,
      "currency_code": "USD"
    },
    "compare_at_price": {
      "amount": 7900,
      "currency_code": "USD"
    },
    "availability": "in_stock",
    "variants": [
      {
        "id": "var_001",
        "attributes": { "size": "8", "color": "White" },
        "sku": "SHOE-001-8-W",
        "price": { "amount": 5900, "currency_code": "USD" },
        "availability": "in_stock"
      },
      {
        "id": "var_002",
        "attributes": { "size": "9", "color": "White" },
        "sku": "SHOE-001-9-W",
        "price": { "amount": 5900, "currency_code": "USD" },
        "availability": "in_stock"
      },
      {
        "id": "var_003",
        "attributes": { "size": "10", "color": "Black" },
        "sku": "SHOE-001-10-B",
        "price": { "amount": 5900, "currency_code": "USD" },
        "availability": "out_of_stock"
      }
    ],
    "shipping": {
      "weight": { "value": 1.8, "unit": "lb" },
      "dimensions": { "length": 13, "width": 8, "height": 5, "unit": "in" },
      "destinations": ["US", "CA", "MX"],
      "free_shipping_threshold": { "amount": 4900, "currency_code": "USD" }
    },
    "return_policy": {
      "returnable": true,
      "return_days": 30,
      "conditions": "Unworn, with tags and original packaging"
    }
  }
}

5.2 Required and Optional Fields

Field	Type	Required	Description
`id`	string	Yes	Unique product identifier
`name`	string	Yes	Product name
`price.amount`	integer	Yes	Price in ISO 4217 minor currency units
`price.currency_code`	string	Yes	ISO 4217 currency code
`availability`	string	Yes	`in_stock` / `out_of_stock` / `preorder`
`images`	array	Yes	At least one product image
`description`	string	No	Product description
`brand`	string	No	Brand name
`category`	string	No	Product category
`sku`	string	No	Stock Keeping Unit
`gtin`	string	No	Global Trade Item Number
`variants`	array	No	Variant list (for multi-option products)
`compare_at_price`	object	No	Original / strikethrough price
`url`	string	No	Product page URL

5.3 Variant Management

Products with multiple options (color, size, material, etc.) use the variants array:

Each variant has its own id, sku, price, and availability
The attributes object defines option attributes as key-value pairs
AI agents can present all available options when displaying a product
Variants can have different prices (e.g., larger sizes at a premium)

5.4 Four Transport Mechanisms

UCP product data can be delivered to AI agents via four transport mechanisms, each suited to different integration scenarios.

REST Transport (OpenAPI 3.x)

The most traditional server-to-server integration approach. Merchants provide a REST API conforming to the OpenAPI 3.x specification:

GET /ucp/catalog/products?query=running+shoes&category=Athletic&limit=10&offset=0
Accept: application/json
Authorization: Bearer {api_key}

GET /ucp/catalog/products/{product_id}
Accept: application/json

REST transport is ideal for merchants and platforms with existing API infrastructure.

MCP Transport (OpenRPC / JSON-RPC 2.0)

An AI-native transport mechanism. UCP exposes catalog tools via the MCP protocol, defined using OpenRPC schemas. Three standard tools are provided: search_catalog — Search the product catalog

{
  "jsonrpc": "2.0",
  "method": "search_catalog",
  "params": {
    "query": "running shoes",
    "filters": {
      "category": "Athletic",
      "price_min": 3000,
      "price_max": 15000,
      "availability": "in_stock"
    },
    "limit": 10,
    "offset": 0
  },
  "id": 1
}

lookup_catalog — Look up by SKU or GTIN

{
  "jsonrpc": "2.0",
  "method": "lookup_catalog",
  "params": {
    "sku": "SHOE-001",
    "gtin": "1234567890123"
  },
  "id": 2
}

get_product — Get single product details

{
  "jsonrpc": "2.0",
  "method": "get_product",
  "params": {
    "product_id": "prod_abc123"
  },
  "id": 3
}

The key advantage of MCP transport is that AI applications (such as Claude or ChatGPT) can directly use UCP merchants as MCP tools without additional integration code. AI agents understand tool definitions through natural language and autonomously decide when to invoke each tool.

A2A Transport (Agent Card Specification)

Designed for multi-agent collaboration scenarios. Merchants publish an Agent Card that enables other AI agents to discover and connect with them. Agent Cards follow Google’s Agent-to-Agent protocol specification. Applicable scenarios include: a shopping agent invoking a payment agent, a price-comparison agent querying multiple merchant agents simultaneously, and similar patterns.

Embedded Transport (OpenRPC Schema)

A transport mechanism for embedded scenarios that uses only the OpenRPC schema (without the full MCP protocol). Suitable for merchants embedding an AI shopping assistant within their own website.

5.5 Transport Comparison

Transport	Schema Format	Authentication	Use Case	Implementation Complexity
REST	OpenAPI 3.x	API Key / OAuth	Server-to-server, platform integration	Low
MCP	OpenRPC (JSON-RPC 2.0)	MCP auth	Direct AI application integration	Medium
A2A	Agent Card Spec	Inter-agent auth	Multi-agent collaboration	Medium
Embedded	OpenRPC schema	In-page auth	Embedded AI assistants	Low

5.6 Price Format Specification

UCP uses integers to represent prices (ISO 4217 minor currency units), avoiding floating-point precision issues:

Currency	currency_code	Exponent	Representation of $59.00 or equivalent
US Dollar	`USD`	2	`5900`
Euro	`EUR`	2	`5900`
Japanese Yen	`JPY`	0	`59`
Kuwaiti Dinar	`KWD`	3	`59000`

Implementation note: Always look up the decimal places for a currency from the ISO 4217 exponent table. Do not hardcode exponent values.

5.7 Search and Filtering

UCP defines standardized search and filter parameters:

Parameter	Type	Description
`query`	string	Full-text search keyword
`category`	string	Category filter
`price_min`	integer	Minimum price (minor currency units)
`price_max`	integer	Maximum price (minor currency units)
`availability`	string	Stock status filter
`brand`	string	Brand filter
`limit`	integer	Results per page (recommended max: 50)
`offset`	integer	Offset for pagination
`sort`	string	Sort order (`price_asc`, `price_desc`, `relevance`)

Next chapter: Security and Authentication — RFC 9421 signatures, JWK keys, mTLS, and Content-Digest

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UCP product data format and transport methods

Product Data and Transports

5.1 Product Data Structure

5.2 Required and Optional Fields

5.3 Variant Management

5.4 Four Transport Mechanisms

REST Transport (OpenAPI 3.x)

MCP Transport (OpenRPC / JSON-RPC 2.0)

A2A Transport (Agent Card Specification)

Embedded Transport (OpenRPC Schema)

5.5 Transport Comparison

5.6 Price Format Specification

5.7 Search and Filtering

​Product Data and Transports

​5.1 Product Data Structure

​5.2 Required and Optional Fields

​5.3 Variant Management

​5.4 Four Transport Mechanisms

​REST Transport (OpenAPI 3.x)

​MCP Transport (OpenRPC / JSON-RPC 2.0)

​A2A Transport (Agent Card Specification)

​Embedded Transport (OpenRPC Schema)

​5.5 Transport Comparison

​5.6 Price Format Specification

​5.7 Search and Filtering

Product Data and Transports

5.1 Product Data Structure

5.2 Required and Optional Fields

5.3 Variant Management

5.4 Four Transport Mechanisms

REST Transport (OpenAPI 3.x)

MCP Transport (OpenRPC / JSON-RPC 2.0)

A2A Transport (Agent Card Specification)

Embedded Transport (OpenRPC Schema)

5.5 Transport Comparison

5.6 Price Format Specification

5.7 Search and Filtering