> ## Documentation Index
> Fetch the complete documentation index at: https://guide.omnia-voice.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Built-in tools

> Platform call control. Attach by name, no configuration.

Built-in tools are maintained by the platform and need no setup. List them:

```bash theme={null}
curl "https://api.omnia-voice.com/api/v1/agent-tools/system" \
  -H "X-API-Key: $OMNIA_API_KEY"
```

| Tool             | What it does                                   |
| ---------------- | ---------------------------------------------- |
| `hangUp`         | Ends the call                                  |
| `playDtmfSounds` | Sends touch tones, for navigating a phone menu |

## `hangUp`

<Warning>
  **Without `hangUp` an agent cannot end a call.** It finishes speaking and
  waits, and the caller sits in silence wondering whether to hang up.

  This is the single most common omission on a first agent. Attach it to
  anything that answers a phone.
</Warning>

The agent decides when the conversation is genuinely over. Reinforce it in the
prompt if callers tend to trail off:

```text theme={null}
When the caller says goodbye or confirms they need nothing else, say goodbye and
end the call.
```

## `playDtmfSounds`

For agents that call *into* another system — pressing 2 for support, entering an
account number at a prompt.

```text theme={null}
When you reach an automated menu, press the option for customer service, then
enter the account number followed by the hash key.
```

<Note>
  Touch tones are a telephony concept. On browser calls the tool exists but has
  nothing to signal.
</Note>

## Attaching

The same call as any other tool — use the `id` from `/agent-tools/system`:

```bash theme={null}
curl -X POST "https://api.omnia-voice.com/api/v1/agents/AGENT_ID/tools" \
  -H "X-API-Key: $OMNIA_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "toolIds": ["HANGUP_TOOL_ID"] }'
```