Every UCP store picks how it speaks to agents: a JSON-RPC MCP server, OpenAPI REST endpoints, an A2A Agent Card, an embedded checkout surface, or a plain redirect hand-off. This is a live map of transport adoption across the stores we monitor, updated every 24 hours.
Model Context Protocol: JSON-RPC tool calls agents use to search, cart, and check out.
OpenAPI REST endpoints with UCP-Agent and Idempotency-Key headers.
Agent-to-Agent: discovery via an Agent Card for agent-native interactions.
Embedded Checkout Protocol: postMessage handshake + CSP frame-ancestors.
Hand-off to a hosted checkout URL when programmatic checkout is unavailable.
We record 25 transport exposures across the verified pool. Our crawler reads each store's UCP manifest and probes the advertised endpoints, attributing a transport only when the handshake actually succeeds. If a store exposes more than one, it counts toward each. Run a live check on any store to see its transports attributed immediately.