ACP discovery

How Hostrail publishes truthful Agentic Commerce Protocol discovery metadata without overstating checkout or payment support.

What Hostrail publishes today

Hostrail publishes ACP discovery metadata on both the root site and the API origin:

GET https://hostrail.dev/.well-known/acp.json
GET https://api.hostrail.dev/.well-known/acp.json

These documents are discovery surfaces, not a second booking API. They tell an agent runtime which commerce service groups the platform already supports through the current REST and MCP lanes.

Current ACP shape

{
  "protocol": {
    "name": "acp",
    "version": "0.1"
  },
  "api_base_url": "https://api.hostrail.dev",
  "transports": ["https+json", "mcp"],
  "transport_endpoints": {
    "https+json": "https://api.hostrail.dev",
    "mcp": "https://mcp.hostrail.dev/mcp"
  },
  "capabilities": {
    "services": ["catalog", "pricing", "reservation", "booking"]
  }
}

Service mapping

ACP service groups are descriptive mappings over the platform's existing surfaces:

ACP service	Current platform capability
`catalog`	Hotel, room type, policy, and machine-readable discovery surfaces
`pricing`	Search and quote flows that return current rates and policy context
`reservation`	Hold creation and release
`booking`	Booking confirmation, retrieval, cancellation, receipts, and guest follow-up

What this does not imply

Publishing acp.json does not mean Hostrail already implements:

an ACP-native checkout session model
ACP-specific payment objects
ACP webhook or event contracts
a second standalone ACP transport beyond the existing REST and MCP lanes

Agents should still execute the real booking flow through:

search
quote
hold
booking confirmation
guest servicing

Recommended agent startup sequence

Fetch https://hostrail.dev/.well-known/api-catalog
Fetch https://hostrail.dev/.well-known/acp.json
Fetch https://api.hostrail.dev/.well-known/agent-card.json
Fetch https://api.hostrail.dev/openapi.json
If using protected API calls, fetch OAuth metadata and mint a bearer before the first live call

When to use ACP discovery vs Agent Card

Use ACP discovery when a runtime wants a coarse commerce-oriented capability map. Use the Agent Card and OpenAPI when the runtime needs exact operation names, request bodies, auth headers, and error semantics.