Protocol
HIGHEach service `transport` is rest, mcp, a2a, or embedded
Each `services[].transport` is one of `rest`, `mcp`, `a2a`, `embedded`. An unrecognised transport leaves agents with no handler to dispatch — your service appears absent.
What this check looks for
Agent runtimes dispatch capability negotiation off the service transport. The UCP overview enumerates exactly four allowed values: `rest`, `mcp`, `a2a`, and `embedded`. Free-form labels (`http`, `graphql`, `soap`) leave agents with no handler — the service is treated as absent. We require every services[] entry to declare a transport in the recognised set.
Which AI surfaces it affects
- Google AI Mode (UCP)80
- Microsoft Copilot60
- ChatGPT (ACP)30
- Perplexity20
- Meta AI20
Weighted against the live specs — ACP 2026-04-17, UCP 2026-04-08.
How to fix it
Set transport to one of rest, mcp, a2a, or embedded
Shopify
A few minutes- Update the UCP JSON your handler emits so every service `transport` matches the UCP enum.
BigCommerce
A few minutes- Edit the edge worker producing the UCP profile to use only recognised transport values.
WooCommerce
A few minutes- Update the UCP JSON file: each service `transport` must be one of rest/mcp/a2a/embedded.
Custom / headless
A few minutes- Replace any free-form transport labels with rest, mcp, a2a, or embedded.
<!-- /.well-known/ucp (excerpt) -->
{
"services": [
{
"namespace": "shopping",
"version": "2026-04-08",
"transport": "rest",
"endpoint": "https://example.com/ucp/shopping"
},
{
"namespace": "returns",
"version": "2026-04-08",
"transport": "a2a",
"endpoint": "https://example.com/ucp/returns"
}
]
}The spec it's pinned to
UCP overview — transport enum
UCP services declare exactly one of four transports: `rest`, `mcp`, `a2a`, `embedded`. Agents dispatch their handlers off this field; any other value leaves the service unreachable.
Does your store pass this check?
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