coordinator-subagent-pattern

coordinator-subagent-pattern

The most common multi-agent ADK 2.0 layout: one coordinator routes user input to specialist subagents.

When to use

• Different user requests need different specialists (billing vs technical)
• You want a single root entry-point that delegates intelligently
• Specialists have distinct tools, instructions, or models

Template

from google.adk.agents import LlmAgent

greeter = LlmAgent(
    name="greeter",
    model="gemini-2.5-flash",
    description="Handles greetings, small talk, and onboarding.",
    instruction="Greet the user warmly. Ask how you can help.",
)

task_executor = LlmAgent(
    name="task_executor",
    model="gemini-2.5-pro",
    description="Executes concrete tasks: search, calculations, file ops.",
    instruction="Carry out the user's task. Cite sources where relevant.",
)

coordinator = LlmAgent(
    name="coordinator",
    model="gemini-2.5-flash",
    description="Routes user requests to greeter or task_executor.",
    instruction=(
        "You coordinate two specialists:\n"
        "  - greeter: small talk, intros\n"
        "  - task_executor: concrete tasks\n"
        "Inspect the user's message and delegate to the right specialist. "
        "Do not answer directly unless neither specialist fits."
    ),
    sub_agents=[greeter, task_executor],
)

root_agent = coordinator

How delegation works

ADK exposes each subagent's name and description to the coordinator's LLM. The coordinator decides via tool-call which subagent receives the next turn.

Best practices

• Give each subagent a distinctive description — that's what the coordinator reads
• Keep coordinator instruction terse; let descriptions do the routing work
• Use cheaper models for routing (flash) and heavier models for execution (pro)
• One layer of nesting is usually enough; avoid coordinator-of-coordinators

Validation

• Each subagent has unique name
• Each subagent has a clear description (≤ 1 sentence is ideal)
• Coordinator instruction lists every subagent
• Test routing with prompts that should hit each specialist