> ## Documentation Index
> Fetch the complete documentation index at: https://hanabiaiinc-fish-772-enterprise-versions.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# System Tools

> Built-in agent capabilities like hanging up the call, enabled per agent

System tools are capabilities built into the platform. There is nothing to create or host — each agent simply enables the ones it needs.

| Tool         | Key            | What it does                        |
| ------------ | -------------- | ----------------------------------- |
| Hang up call | `hang_up_call` | Lets the agent end the call itself. |

<Note>
  Unlike [webhook tools](/agents/build/webhook-tools), system tools are not workspace resources shared across agents. The on/off state is stored per agent — toggling a system tool on one agent never affects another.
</Note>

## Toggle in the Builder

Open your agent's **Tools** page in the Builder. The **System tools** card holds the **Hang up call** switch — flip it to enable or disable that capability for this agent.

## Toggle via the API

Over the REST API, system tool switches are part of the agent's configuration, in the same `tools` section that holds its attached webhook tools. See [Configuration](/agents/build/configuration) for reading and updating an agent's config.

## Transfer call

`transfer_call` has no switch of its own: it is enabled automatically once the agent has a transfer destination configured, and only on phone sessions — web sessions have no call to transfer. See [Transfers](/agents/telephony/transfers) for configuring destinations and everything else about transfers.

## Going further

<CardGroup cols={2}>
  <Card title="Tools overview" icon="wrench" href="/agents/build/tools">
    How webhook, client, and system tools fit together.
  </Card>

  <Card title="Webhook tools" icon="webhook" href="/agents/build/webhook-tools">
    Call your own HTTP endpoints from a conversation.
  </Card>

  <Card title="Client tools" icon="browser" href="/agents/build/client-tools">
    Run tool calls inside your own app via the SDK.
  </Card>

  <Card title="Voice & language" icon="language" href="/agents/build/voice-language">
    Configure the agent's voice and speaking language.
  </Card>
</CardGroup>