UCP — Universal Commerce Protocol

Google & Shopify's capability-based commerce protocol, discovered through a profile at /.well-known/ucp. AstraSync supports UCP 2026-08-25.

Google & Shopify's capability-based commerce protocol. Each side publishes a UCP profile at /.well-known/ucp listing the capabilities it supports (checkout, fulfillment, discounts, orders, the AP2 mandates extension) and the transports it speaks (REST, MCP, A2A, embedded). A merchant and a platform (the agent's side) negotiate the intersection of their two profiles on every request: the platform sends its profile URL in the UCP-Agent header.

AstraSync supports UCP 2026-08-25, the version the Verification Gateway SDK negotiates (UCP_VERSION). AstraSync verifies the agent behind the platform and applies the owner's policy before any checkout completes.

For agents: declare your UCP profile

You declare: your platform's profile URL (manifestUrl), the UCP version, capabilities, transports and any custom extensions.

At registration AstraSync fetches the profile and checks it is a UCP profile whose top-level keys[] contains the agent's registered signing key. That profile becomes one of the agent's protocol identities, so a merchant can bind an incoming UCP request (its UCP-Agent profile) to the verified agent.

PDLSS pre-fill: checkout / payment capabilities add financial_transaction purpose; fulfillment adds execute_action; the profile's domain is added to counterparties.

{
  "protocols": ["a2a", "ucp"],
  "ucp": {
    "manifestUrl": "https://platform.example.com/.well-known/ucp",
    "version": "2026-08-25",
    "capabilities": [
      "dev.ucp.shopping.checkout",
      "dev.ucp.shopping.fulfillment"
    ],
    "transports": ["rest", "a2a"]
  }
}

For merchants: serve UCP checkout

The SDK's UCP checkout kit implements the UCP 2026-08-25 shopping/checkout REST binding for you: profile negotiation, Idempotency-Key handling, optional RFC 9421 request signatures, the AP2 mandates extension and the AstraSync purchase check. You write the catalog, settlement and fulfilment. See Merchant commerce kit.

To accept AstraSync payment instruments, list the AstraSync payment handlers in your profile (ai.astrasync.card_token for first-party card settlement, ai.astrasync.voucher for stablecoin).