ap2-a2a-extension

AP2 as an A2A Extension

Before writing code

Fetch live docs:

1. Fetch https://ap2-protocol.org/specification/ for the A2A extension specification
2. Fetch https://ap2-protocol.org/topics/ap2-a2a-and-mcp/ for protocol integration details
3. Web-search site:github.com google-agentic-commerce AP2 a2a extension for reference implementation
4. Web-search site:github.com google-agentic-commerce AP2 samples a2a for A2A-based samples

Conceptual Architecture

AP2 Extends A2A

AP2 is designed as a direct extension of the A2A protocol. It adds payment-specific capabilities to A2A's general-purpose agent-to-agent communication:

• A2A provides: tasks, messages, parts, streaming, agent cards
• AP2 adds: mandates, payment flows, VDCs, cryptographic signing, risk signals

Why A2A is Required

As the documentation states: "A2A is required to standardize intra-agent communication — as soon as you have more than one agent you need A2A." AP2 adds payment standardization on top.

How AP2 Rides on A2A

Agent Cards with AP2 Capabilities

AP2 agents declare payment support in their Agent Card:

{
  "name": "MerchantAgent",
  "capabilities": {
    "extensions": [
      {
        "description": "AP2 Payment Extension",
        "required": true,
        "uri": "https://ap2-protocol.org/extension/v1"
      }
    ]
  },
  "skills": [
    {
      "id": "checkout",
      "name": "Cart and Payment",
      "description": "Handles product search and cart creation",
      "tags": ["ap2", "payment", "commerce"]
    }
  ],
  "security": [...],
  "securitySchemes": {...}
}

Mandates as A2A DataParts

AP2 mandates are transmitted as DataParts within A2A messages:

• Intent Mandate → DataPart in message from Shopping Agent to Merchant
• Cart Mandate → DataPart in response from Merchant to Shopping Agent
• Payment Mandate → DataPart in payment flow messages

A2A Tasks for Payment Flows

Each phase of the AP2 flow maps to A2A tasks:

• Product search → A2A task (SA → Merchant)
• Payment method query → A2A task (SA → CP)
• Payment processing → A2A task (Merchant → MPP)
• Challenge handling → A2A messages within existing tasks