Universal Commerce Protocol (UCP)

The Universal Commerce Protocol is an open standard for agentic commerce, launched by Shopify and Google. It defines how AI agents interact with e-commerce platforms in a standardized, secure way.

Guardrail-sim is UCP-ready, meaning it produces responses that conform to UCP specifications and can integrate directly into UCP-compliant checkout flows.

Why UCP Matters

As AI agents increasingly handle commerce tasks—from comparison shopping to discount negotiation—there needs to be a common language for:

• Validating discount codes with standard error codes
• Allocating discounts across line items consistently
• Managing checkout sessions with predictable state flows

Guardrail-sim provides the policy enforcement layer that sits between AI agents and your commerce backend.

UCP Discount Extension

The UCP Discount Extension defines how discounts are applied and communicated. Guardrail-sim supports:

Error Codes

When a discount is rejected, we return UCP-standard error codes:

Allocations

Discounts can be distributed across line items using two methods:

• across: Proportional allocation based on item subtotals
• each: Even split across all items

import { calculateAllocations } from '@guardrail-sim/policy-engine';
 
const allocations = calculateAllocations(1000, lineItems, 'across');
// [
//   { target: '$.line_items[0]', amount: 750 },
//   { target: '$.line_items[1]', amount: 250 },
// ]

MCP Tools for UCP

The guardrail-sim MCP server exposes UCP-aligned tools:

validate_discount_code

Pre-validate a discount code before applying it to a checkout:

// Input
{
  code: 'SUMMER20',
  order: { order_value: 5000, quantity: 50, product_margin: 0.4 },
  proposed_discount: 0.2
}
 
// Output
{
  valid: false,
  error_code: 'discount_code_user_ineligible',
  message: 'Discount exceeds tier limit (10% base, 15% for qty >= 100)'
}

simulate_checkout_discount

Simulate a full checkout with discounts:

// Input
{
  codes: ['SUMMER20'],
  line_items: [
    { item_id: 'SKU-001', quantity: 2, subtotal: 5000, product_margin: 0.4 }
  ],
  proposed_discount: 0.1
}
 
// Output
{
  applied: [{
    code: 'SUMMER20',
    amount: 500,
    method: 'across',
    allocations: [{ target: '$.line_items[0]', amount: 500 }]
  }],
  rejected: [],
  messages: []
}

UCP Types Package

For TypeScript users, import UCP types directly:

import type {
  DiscountErrorCode,
  AppliedDiscount,
  DiscountAllocation,
  CheckoutStatus,
} from '@guardrail-sim/ucp-types';
 
import {
  toUCPErrorCode,
  buildDiscountExtensionResponse,
  calculateAllocations,
} from '@guardrail-sim/ucp-types/converters';

Platform Compatibility

Guardrail-sim's UCP implementation is compatible with:

Resources

• UCP Specification
• UCP GitHub Repository
• UCP Conformance Tests