> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fish.audio/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.
</Note>

## Toggle in the Builder

Open your agent's **Tools** page in the Builder. The **System tools** card holds the **Hang up call** switch.

## 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>