# `ADK.Tool.TransferToAgent`
[🔗](https://github.com/zeroasterisk/adk-elixir/blob/main/lib/adk/tool/transfer_to_agent.ex#L1)

Built-in tool that enables an agent to transfer control to a sub-agent.

When an LLM agent has sub-agents configured, `transfer_to_agent` tools are
automatically generated — one per sub-agent. When the LLM calls this tool,
it produces an event with `actions.transfer_to_agent` set, which the runner
picks up to hand off execution to the target agent.

## Differences from Python ADK

Python ADK creates a single `transfer_to_agent` tool with an enum constraint
on the `agent_name` parameter. Elixir creates one tool per target agent
(named `transfer_to_agent_<name>`) with the target hardcoded in the closure.

Both approaches prevent hallucinated agent names:
- Python: enum constraint restricts valid values
- Elixir: separate tools mean the LLM picks the right tool by name, no
  parameter to hallucinate

The per-agent approach was chosen for Elixir because:
1. It eliminates a class of errors (wrong agent_name parameter)
2. Tool descriptions per-agent give the LLM better context for selection
3. It works naturally with Elixir's pattern matching

## How it works

1. The parent agent's tool list is augmented with one `transfer_to_agent_*`
   tool per sub-agent
2. When the LLM invokes the tool, it returns a transfer event
3. The parent agent's run loop detects the transfer and delegates to the
   target sub-agent
4. The sub-agent runs and its events are returned

# `target_agent`

```elixir
@spec target_agent({:transfer_to_agent, String.t()}) :: String.t()
```

Extract the target agent name from a transfer result.

# `tools_for_sub_agents`

```elixir
@spec tools_for_sub_agents([ADK.Agent.t()]) :: [ADK.Tool.FunctionTool.t()]
```

Generate transfer tools for a list of target agents.

Returns a list of `ADK.Tool.FunctionTool` structs, one per target agent.
Each tool's parameters include an `enum` constraint on the `agent_name`
field listing all valid target names, preventing the LLM from hallucinating
non-existent agent names.

# `transfer?`

```elixir
@spec transfer?(term()) :: boolean()
```

Check if a tool result is a transfer signal.

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*Consult [api-reference.md](api-reference.md) for complete listing*