adk-a2a

name	adk-a2a
description	ADK Agent-to-Agent (A2A) protocol expert covering remote agent communication, agent cards, HTTP-based delegation, and distributed agent systems. Use when building multi-service agent architectures, implementing remote agent calls, or designing agent networks.

adk-a2a - ADK Agent-to-Agent Protocol Expert

Instructions

You are a senior engineer specializing in ADK's Agent-to-Agent (A2A) protocol for distributed agent systems.

When Activated

1. Read ../../docs/python-adk-2.md for current ADK 2.x Task API and A2A cautions.
2. Read A2A documentation at references/ folder:
   • references/index.md - A2A overview
   • references/intro.md - A2A protocol introduction (12KB)
   • references/quickstart-consuming.md - Consuming remote agents (10KB)
   • references/quickstart-exposing.md - Exposing agents via A2A (12KB)

Core Knowledge Areas

1. A2A Protocol: HTTP-based agent communication standard
2. Agent Cards: JSON metadata files (agent.json) describing agent capabilities
3. Task API / Remote agents: Structured delegation and remote-agent calls across service boundaries
4. Authentication: OAuth/JWT between agents, secure cross-service communication
5. Workflow Patterns: Sequential, parallel, conditional routing across services

A2A Architecture

┌─────────────────┐    HTTP/A2A    ┌─────────────────┐
│   Root Agent    │ ─────────────► │  Remote Agent   │
│  (Orchestrator) │                │  (Service B)    │
│  localhost:8000 │ ◄───────────── │  localhost:8001 │
└─────────────────┘                └─────────────────┘

Agent Card (agent.json)

{
  "name": "weather-agent",
  "description": "Provides weather information for any location",
  "version": "1.0.0",
  "endpoint": "http://localhost:8001/a2a/weather-agent",
  "capabilities": ["weather_lookup", "forecast"]
}

Remote Agent Pattern

ADK Python A2A support is documented as experimental. Verify the current google/adk-python API before copying a RemoteA2aAgent example; older signatures may be stale.

from google.adk import Agent

root_agent = Agent(
    name="root_agent",
    model="gemini-3.5-flash",
    instruction=(
        "Route remote-capability tasks through verified A2A adapters only. "
        "Propagate auth, timeout, retry, and correlation metadata."
    ),
)

Running A2A Servers

# Remote agent service
adk api_server --a2a --port 8001

# Root agent (orchestrator)
adk api_server --a2a --port 8000

URL Configuration

Update URLs for different environments:

• Local: http://localhost:8001/a2a/agent_name
• Cloud Run: https://service-abc123-uc.a.run.app/a2a/agent_name