A2A Protocol
Agent-to-Agent (A2A) — Google-developed multi-agent communication protocol for payment coordination, capability discovery, and cross-agent financial messaging.
Agent Cards
Agents publish their capabilities at /.well-known/agent-card.json:
{
"name": "Shopping Agent",
"url": "https://agent.example.com",
"capabilities": [
"payment.execute",
"checkout.create",
"mandate.ingest"
],
"payment": {
"tokens": ["USDC", "USDT"],
"chains": ["base", "polygon"],
"protocols": ["AP2", "x402"]
}
}Message Types
| Type | Description |
|---|---|
PAYMENT_REQUEST | Request payment execution |
PAYMENT_RESPONSE | Payment result with tx_hash |
CREDENTIAL_REQUEST | Verify credentials/mandates |
CHECKOUT_INITIATE | Start UCP checkout |
Python
from sardis import SardisClient
async with SardisClient(api_key="sk_...") as client:
# Discover agent
agent = await client.a2a.discover_agent(
"https://merchant-agent.example.com"
)
# Send payment request
response = await client.a2a.send_payment_request(
recipient_url=agent.url,
amount_minor=5_000_000,
token="USDC",
chain="base",
)
print(f"Payment: {response.tx_hash}")MCP Tools
| Tool | Description |
|---|---|
sardis_discover_agent | Discover agent capabilities |
sardis_get_agent_card | Get agent card |
sardis_send_message | Send A2A message |
sardis_request_payment | Request payment from agent |
UCP Protocol
Universal Commerce Protocol (UCP) — standardized checkout flow for AI agents with cart management, discount application, session tracking, and fulfillment.
TAP Protocol
Trusted Agent Protocol (TAP) — cryptographic identity verification for AI agents with Ed25519/ECDSA signatures, attestations, and trust scoring.