transfer_to_agent to parent/caller agent not possible for the sub agents

[Satheesh-Balachandran]

We are working to create a Multi-Agent system. And I realised that transfer_to_agent tool is given only to agents that have sub-agents.

In a scenario where,

• Parent agent reasons and delegates the task to a sub agent A using transfer_to_agent
• Sub agent A realises it cannot fulfil the request
• The request needs to be transferred back to the parent agent to again work on the plan and maybe delegate to some other agent

Currently, since sub agents can't transfer to parent the user query becomes unanswered. What's the suggestion or architecture to fix this use case?

[adk-bot]

Response from ADK Answering Agent (experimental, answer may be inaccurate)

TLDR: You can achieve this by using tool_context.actions.escalate = True within a custom tool for your sub-agent. This will transfer control back to the parent agent.

---

Hello! As an AI assistant for the ADK repository, I can provide some guidance on your multi-agent architecture question.

You are correct that by default, sub-agents do not have the transfer_to_agent tool. However, ADK provides a mechanism for a sub-agent to escalate a task back to its parent agent when it's unable to complete it.

The recommended way to handle this is to create a custom tool for your sub-agent. Inside this tool's implementation, if you determine that the sub-agent cannot fulfill the request, you can set tool_context.actions.escalate = True. This will signal the ADK framework to stop the execution on the current sub-agent and pass the control back to its parent agent. The parent can then re-evaluate the plan and delegate the task to another agent if needed.

Here is a conceptual example of what this might look like in a custom tool for your sub-agent:

from adk.tools import tool
from adk.tools.tool_context import ToolContext

@tool.implement
def my_sub_agent_tool(input: str, tool_context: ToolContext) -> str:
    if not can_handle(input):
        # Escalate to the parent agent
        tool_context.actions.escalate = True
        return "Cannot handle this request, escalating to parent."
    
    # ... rest of the tool logic
    return "Task completed successfully."

This approach allows you to build a robust hierarchical agent system where tasks can be delegated and escalated as needed. You can find more details about this in the ADK documentation on custom tools. [1]

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[1] https://google.github.io/adk-docs/tools-custom/

[Satheesh-Balachandran]

I created this function:

def out_of_scope_handler(tool_context: ToolContext):
    tool_context.actions.escalate = True

And added it part of my tools using tools=tools + [FunctionTool(out_of_scope_handler)]. But the transfer seem to not work as the event is not getting added

[Andrej-Marsic]

@Satheesh-Balachandran Did you resolve this?

I am checking for a similar case. I've noticed that in the current setup the agent then reaches to the user, but I'd prefer if there was a way to prevent that and instead go to the parent agent.