> ## 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 — language detection, hang up call, and call transfer — 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                                             |
| ------------------ | -------------------- | -------------------------------------------------------- |
| Language detection | `language_detection` | Lets the agent detect the language the user is speaking. |
| Hang up call       | `hang_up_call`       | Lets the agent end the call itself.                      |
| Transfer call      | `transfer_call`      | Lets the agent hand a live phone call to another number. |

<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. The **Language detection** switch lives on the agent's **Configuration** page, next to **Speaking language** — see [Voice & language](/agents/build/voice-language). Flip a switch 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>