A2A

Overview

A2A (Agent-to-Agent) protocol enables direct communication between AI agents for complex commerce scenarios. Multiple agents can coordinate to compare prices, negotiate terms, and complete transactions autonomously.

A2A Endpoint Discovery

A2A endpoints are declared in the business profile:

{
  "transports": {
    "a2a": {
      "endpoint": "https://a2a.business.com",
      "protocol_version": "1.0",
      "capabilities": ["negotiation", "multi-item", "scheduling"]
    }
  }
}

Message Format

{
  "type": "a2a.commerce.request",
  "id": "msg_unique_123",
  "from": {
    "type": "agent",
    "identifier": "agent:buyer-assistant-001",
    "name": "Shopping Assistant"
  },
  "to": {
    "type": "agent",
    "identifier": "agent:store-agent-acme",
    "name": "ACME Store Agent"
  },
  "conversation_id": "conv_abc123",
  "timestamp": "2025-01-15T10:30:00Z",
  "payload": {
    "intent": "purchase",
    "items": [
      { "sku": "WH-PRO-001", "quantity": 1 }
    ],
    "constraints": {
      "max_total": 250.00,
      "currency": "USD",
      "delivery_by": "2025-01-20"
    },
    "mandate_ref": "mandate_xyz789"
  }
}

Conversation Flow

Message Types

Purchase Intent

{
  "type": "a2a.commerce.intent",
  "payload": {
    "intent": "purchase",
    "items": [
      { "sku": "WH-PRO-001", "quantity": 1 }
    ],
    "constraints": {
      "max_total": 250.00,
      "delivery_by": "2025-01-20"
    }
  }
}

Quote Response

{
  "type": "a2a.commerce.quote",
  "payload": {
    "quote_id": "quote_abc123",
    "valid_until": "2025-01-15T11:30:00Z",
    "items": [
      {
        "sku": "WH-PRO-001",
        "name": "Pro Wireless Headphones",
        "unit_price": 149.99,
        "quantity": 1,
        "availability": "in_stock"
      }
    ],
    "totals": {
      "subtotal": 149.99,
      "shipping": 9.99,
      "tax": 14.40,
      "total": 174.38
    },
    "delivery_estimate": "2025-01-18"
  }
}

Acceptance

{
  "type": "a2a.commerce.accept",
  "payload": {
    "quote_id": "quote_abc123",
    "mandate_proof": {
      "mandate_id": "mandate_xyz789",
      "transaction_hash": "sha256:...",
      "signature": "base64..."
    },
    "shipping_address": {
      "line1": "123 Main St",
      "city": "San Francisco",
      "state": "CA",
      "postal_code": "94102",
      "country": "US"
    }
  }
}

Order Confirmation

{
  "type": "a2a.commerce.confirmation",
  "payload": {
    "order_id": "ord_xyz789",
    "status": "confirmed",
    "items": [...],
    "totals": {...},
    "tracking": {
      "url": "https://business.com/track/ord_xyz789"
    }
  }
}

Negotiation Protocol

A2A supports optional negotiation for flexible commerce:

// Counter-offer from buyer
{
  "type": "a2a.commerce.counter",
  "payload": {
    "quote_id": "quote_abc123",
    "proposed_changes": {
      "max_total": 160.00,
      "reason": "Budget constraint"
    }
  }
}

// Store response
{
  "type": "a2a.commerce.quote",
  "payload": {
    "quote_id": "quote_def456",
    "replaces": "quote_abc123",
    "items": [...],
    "totals": {
      "total": 159.99  // Adjusted price
    },
    "note": "Applied 10% discount"
  }
}

Multi-Agent Coordination

Buyer agents can query multiple stores simultaneously:

// Parallel quote requests
const stores = ['store-a', 'store-b', 'store-c'];

const quotes = await Promise.all(
  stores.map(store =>
    a2aClient.send({
      type: 'a2a.commerce.intent',
      to: `agent:${store}`,
      payload: {
        intent: 'quote',
        items: [{ sku: 'WH-PRO-001', quantity: 1 }]
      }
    })
  )
);

// Select best quote
const bestQuote = quotes.reduce((best, quote) =>
  quote.payload.totals.total < best.payload.totals.total
    ? quote : best
);

Error Handling

{
  "type": "a2a.commerce.error",
  "payload": {
    "code": "ITEM_UNAVAILABLE",
    "message": "Product WH-PRO-001 is out of stock",
    "reference": "quote_abc123",
    "alternatives": [
      { "sku": "WH-PRO-002", "name": "Pro Wireless Headphones V2" }
    ]
  }
}

Security

• Message signing - All messages are cryptographically signed
• Agent identity - Verified agent identifiers
• Mandate validation - Transaction authorization checked
• Replay protection - Nonces prevent duplicate processing

Next Steps

• Learn about Embedded Transport for hybrid flows
• See AP2 Mandates for authorization
• Explore AI Agent Integration for implementation