# What is the Universal Commerce Protocol (UCP)?

> The Universal Commerce Protocol lets software agents search a store and build a cart through one standard interface. Definition and a worked example.

Updated 2026-11-06. Source: https://atta.sh/glossary/universal-commerce-protocol

The Universal Commerce Protocol, or UCP, is an open interface for stores to describe their catalog and carts to software agents. An agent can search products and create a cart on any store that speaks it, without a custom integration for each shop.

## Example

An agent looks for 3 desk lamps at a store that supports UCP. It fetches the store's UCP profile, searches for "desk lamp", gets 5 products with prices, and calls `create_cart` with 3 units of one of them. The store returns a cart URL. The agent doesn't pay; the buyer opens the link and checks out.

## In Atta

Atta shops UCP stores for search, headless reads and a store-built cart. The cart written from our servers is the store's anonymous `create_cart`: it carries nothing about the shopper except their country, and only the store's message codes come back, never its text.

A store's own search receives the model's query and its cart receives the model's lines, so Atta sends them only to a store the person named. A card purchase never builds one. Every URL goes through the public-URL check first. The agent hands back the store's cart link, and the shopper checks out at the store.

## What it replaces

Without a shared protocol an agent needs a custom connector for each store, or has to read web pages and guess. A store that publishes its profile can be searched and carted by any agent that speaks the protocol, and the store still controls the checkout.

## Questions

### Is UCP the same as MCP?

No. UCP describes stores and carts. MCP connects a model to tools and data.