Universal Commerce Protocol (UCP)

The Universal Commerce Protocol is an open standard for agentic commerce, announced on 11 January 2026 at NRF by Google, Shopify, Etsy, Wayfair, Target and Walmart, with 20+ endorsing partners including Adyen, American Express, Mastercard, Stripe and Visa. 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/ucp-types';

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