Agent-to-Agent (A2A) Protocol
Multi-Agent Commerce Coordination
The Challenge
Shopping Agent Payment Agent Fulfillment Agent
│ │ │
│ "I need help │ │
│ with payment" │ │
│ ?─────────────? │
│ │ │
│ How do agents discover each other? │
│ How do they share transaction context? │
│ How do they coordinate securely? │
Multi-agent commerce requires standardized coordination.
The Solution: A2A Protocol
Shopping Agent UCP Server Payment Agent
│ │ │
│ 1. Register │ │
│ ──────────────────────> │ <───────────────────│
│ │ 2. Register │
│ │ │
│ 3. Resolve("payment") │ │
│ ──────────────────────> │ │
│ <── [Payment Agent] ── │ │
│ │ │
│ 4. Create Handoff ─────────────────────────────>│
│ <───────────────── 5. Accept ──────────────────│
│ <───────────────── 6. Complete ────────────────│
Agent Card
Every agent has a discoverable identity:
{
"id": "ucp-wix-agent",
"name": "Pop Stop Drink UCP Agent",
"version": "1.0.0",
"capabilities": [
"catalog_search", "cart_management",
"checkout", "payment_handlers"
],
"endpoints": {
"base": "https://wix-ucp-tpa.onrender.com",
"mcp": ".../mcp",
"a2a": ".../a2a"
},
"trust": { "level": "verified" }
}
Agent Discovery
List all known agents:
GET /a2a/agents
Find agents by capability:
POST /a2a/resolve
{ "capability": "payment_processing" }
Response:
{
"agents": [
{ "id": "payment-agent", "name": "Payment Processor", ... }
]
}
Agent Registration
Register an external agent:
POST /a2a/agents
{
"id": "my-custom-agent",
"name": "Custom Shopping Agent",
"version": "1.0.0",
"capabilities": ["checkout", "support"],
"endpoints": { "base": "https://my-agent.com" },
"trust": { "level": "sandbox" }
}
Response: 201 Created
Transaction Handoff
Delegate a transaction to another agent:
POST /a2a/handoff
{
"targetAgentId": "payment-agent",
"type": "checkout",
"context": {
"checkoutId": "checkout-123",
"cartId": "cart-456"
},
"intent": "Complete the payment process",
"permissions": ["read", "execute"],
"ttlSeconds": 3600
}
Handoff Response
{
"success": true,
"handoff": {
"id": "handoff_abc123",
"status": "pending",
"sourceAgent": { "id": "shopping-agent", "name": "..." },
"targetAgent": { "id": "payment-agent", "name": "..." },
"context": { "checkoutId": "checkout-123" },
"intent": "Complete the payment process",
"permissions": ["read", "execute"],
"expiresAt": "2026-01-19T00:00:00Z"
}
}
Handoff Flow
┌──────────────────────────────────────────────────────┐
│ │
│ PENDING ──────> ACCEPTED ──────> COMPLETED │
│ │ │ │
│ │ └──────> FAILED │
│ │ │
│ └──────────> REJECTED │
│ │ │
│ └──────────> EXPIRED (after TTL) │
│ │
└──────────────────────────────────────────────────────┘
Accept a Handoff
Target agent accepts the delegation:
POST /a2a/handoff/handoff_abc123/accept
X-Agent-Id: payment-agent
{ "accept": true }
Response:
{
"success": true,
"handoff": { "status": "accepted", ... }
}
Complete a Handoff
After completing the work:
POST /a2a/handoff/handoff_abc123/complete
X-Agent-Id: payment-agent
{
"status": "completed",
"result": { "orderId": "order-789", "transactionId": "txn-456" }
}
Response:
{
"success": true,
"handoff": { "status": "completed", ... }
}
Security: Permissions
| Permission | Allows |
|---|---|
read |
View checkout/order data |
write |
Modify checkout data |
execute |
Complete transactions |
delegate |
Pass to another agent |
{ "permissions": ["read", "execute"] }
Principle of least privilege - grant only what's needed.
Security: Trust Levels
| Level | Description |
|---|---|
sandbox |
Testing only, no real transactions |
verified |
Identity confirmed |
trusted |
Full production access |
POST /a2a/resolve
{ "capability": "checkout", "minTrustLevel": "verified" }
Security: Time-Limited
Handoff Created Expires
│ │
│ ←────── TTL (1-24 hours) ──────→ │
│ │
▼ ▼
┌─────────┐ ┌─────────┐
│ PENDING │ │ EXPIRED │
│ Active │ │ Invalid │
└─────────┘ └─────────┘
Handoffs auto-expire if not processed.
API Summary
| Method | Endpoint | Purpose |
|---|---|---|
| GET | /a2a/agent |
Self agent card |
| GET | /a2a/agents |
List all agents |
| POST | /a2a/agents |
Register agent |
| POST | /a2a/resolve |
Find by capability |
| POST | /a2a/handoff |
Create handoff |
| GET | /a2a/handoff/:id |
Get handoff |
| POST | /a2a/handoff/:id/accept |
Accept/reject |
| POST | /a2a/handoff/:id/complete |
Complete |
Use Case: Multi-Agent Checkout
┌─────────────┐ ┌─────────────┐ ┌─────────────┐
│ Shopping │ │ Payment │ │ Fulfillment │
│ Agent │ │ Agent │ │ Agent │
└──────┬──────┘ └──────┬──────┘ └──────┬──────┘
│ │ │
│ 1. Create cart │ │
│ 2. Create checkout│ │
│ │ │
│ ── Handoff ────> │ │
│ │ 3. Process payment│
│ <─ Complete ──── │ │
│ │ │
│ ─────────── Handoff ────────────────> │
│ │ │ 4. Ship
│ <────────── Complete ──────────────── │
│ │ │
Live Demo
Get agent card:
curl https://wix-ucp-tpa.onrender.com/a2a/agent
Create a handoff:
curl -X POST https://wix-ucp-tpa.onrender.com/a2a/handoff \
-H "Content-Type: application/json" \
-d '{
"targetAgentId": "test-agent",
"type": "checkout",
"context": {"checkoutId": "test-123"},
"intent": "Test handoff"
}'
Integration with MCP
A2A works alongside MCP tools:
{
"bindings": {
"mcp": {
"tools": "/mcp/tools",
"call": "/mcp/call"
},
"a2a": {
"agent": "/a2a/agent",
"handoff": "/a2a/handoff"
}
}
}
MCP: Execute UCP operations A2A: Coordinate between agents
Summary
┌────────────────────────────────────────────────────┐
│ │
│ 🤖 + 🤖 = 🤝 Agent-to-Agent Coordination │
│ │
│ ✅ Agent discovery by capability │
│ ✅ Secure transaction handoffs │
│ ✅ Permission-based delegation │
│ ✅ Time-limited with auto-expiry │
│ ✅ Trust levels for production safety │
│ ✅ Complete audit trail │
│ │
└────────────────────────────────────────────────────┘
Multi-agent commerce, made simple.
Agent-to-Agent (A2A) Protocol
By Itay Shmool
Agent-to-Agent (A2A) Protocol
Discover the innovative Agent-to-Agent (A2A) Protocol that revolutionizes multi-agent commerce coordination, featuring exciting use cases, live demos, and robust security measures. Explore how seamless agent interactions can enhance your business operations!
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