How to build an agent with Google ADK

Create a function tool

Google ADK can infer a tool schema from a typed Python function and its documentation. Keep the function deterministic and return structured results.

def get_order_status(order_id: str) -> dict:
    """Return the current status for an order."""
    return orders.get_status(order_id)

Configure the agent

Create an agent with a focused instruction and explicitly pass the tools it may use.

from google.adk.agents import Agent

root_agent = Agent(
    name="order_support",
    model="gemini-2.5-flash",
    instruction="Answer order questions using verified tool results.",
    tools=[get_order_status],
)

Add governance before writes

Treat tool schemas as an interface, not a security boundary. Validate identity and permission at execution time, log each call, and place cancellation or refund tools behind human approval.