UCPStoreDocs
Communication Protocols

Transports

Transports define how platforms, agents, and businesses communicate using UCP. Choose the transport that best fits your integration scenario.

Transport Selection

UCP supports multiple transport protocols to accommodate different integration scenarios. The choice of transport depends on your use case:

  • REST - Use for traditional platform integrations and server-to-server communication
  • MCP - Use when integrating UCP into LLM-based applications
  • A2A - Use for fully autonomous agent-to-agent commerce
  • Embedded - Use when human interaction is required during the flow

Available Transports

REST

Primary

HTTP/HTTPS primary transport for direct API integration. Best for server-to-server communication and traditional platform integrations.

Key Features

  • Standard HTTP methods (GET, POST, PUT, DELETE)
  • JSON request/response format
  • OAuth 2.0 authentication
  • Webhook support for async events
  • Rate limiting and retry policies
View documentation

MCP

AI-Native

Model Context Protocol for LLM tool integration. Enables AI models to interact with UCP endpoints as native tools.

Key Features

  • Native LLM tool integration
  • Structured input/output schemas
  • Context-aware responses
  • Streaming support
  • Error handling patterns
View documentation

A2A

Autonomous

Agent-to-Agent protocol for autonomous multi-agent commerce. Enables complex orchestration between AI agents.

Key Features

  • Multi-agent coordination
  • Asynchronous messaging
  • State machine patterns
  • Conflict resolution
  • Audit trail logging
View documentation

Embedded

Hybrid

iframe/webview integration for hybrid experiences. Combines autonomous flow with human-in-the-loop interactions.

Key Features

  • Secure iframe embedding
  • PostMessage communication
  • Session handoff support
  • Mobile webview compatible
  • Fallback UI patterns
View documentation

Transport Declaration

Businesses declare supported transports in their profile:

{
  "transports": {
    "rest": {
      "base_url": "https://api.example.com/ucp/v1",
      "auth_url": "https://auth.example.com/oauth"
    },
    "mcp": {
      "server_url": "https://mcp.example.com",
      "tools_manifest": "https://mcp.example.com/tools.json"
    },
    "a2a": {
      "endpoint": "https://a2a.example.com",
      "protocol_version": "1.0"
    },
    "embedded": {
      "checkout_url": "https://checkout.example.com/embed",
      "allowed_origins": ["https://partner.com"]
    }
  }
}

Transport Interoperability

All transports expose the same underlying capabilities and extensions. A checkout session created via REST can be completed via Embedded, and order events will be delivered via webhooks regardless of the originating transport.

Next Steps

Learn about each transport in detail:

ExtensionsIntegration: Businesses
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