***

title: Overview
subtitle: Cartesia Line Agents in VoxEngine
-------------------------------------------

## Benefits

The native Cartesia module connects Voximplant calls to Cartesia Line Agents for real-time, speech-to-speech conversations.
This allows one agent design to power calls across SIP trunks, WhatsApp, PSTN numbers, and app users while VoxEngine keeps call routing and control.

Capability and feature highlights:

* Connect inbound and outbound calls to one Cartesia Line Agent
* Bi-directional media streaming with telephony-ready audio format support
* Barge-in support via clear events and media buffer control
* Real-time agent events for ACK, custom metadata, DTMF, and diagnostics

## Demo video

Cartesia Line Agents demo:

<iframe width="100%" height="360" src="https://www.youtube.com/embed/5tg83Xl2p5M" title="Cartesia Line Agents demo" frameBorder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" allowFullScreen />

## Architecture

![Cartesia Line Agents architecture](https://files.buildwithfern.com/voximplant.docs.buildwithfern.com/6e3e6086d7343023896cf1283a3372db19e71922b33485632dccdcf240f035e3/docs/assets/diagrams/cartesia-line-agent-architecture.jpg)

## Prerequisites

* Create a Cartesia Line Agent in the [Cartesia Voice Agents portal](https://play.cartesia.ai/agents)
* Cartesia API key from the [Cartesia Platform portal](https://play.cartesia.ai/keys)
* Cartesia agent ID from the [Cartesia Voice Agents portal](https://play.cartesia.ai/agents)
* Inbound or outbound routing configured in Voximplant - see our [getting started guides](/getting-started/) and the [walkthrough video above](#demo-video) for details.

## Development notes

* **Native VoxEngine module**: load `require(Modules.Cartesia)` and create a `Cartesia.AgentsClient` via `Cartesia.createAgentsClient({ apiKey, agentId, cartesiaVersion, ... })`.
* **Line Agent → VoxEngine coordination**: handle `AppEvents.HttpRequest` in your scenario to process `POST` messages sent by your Cartesia Line script for tool-call orchestration and routing decisions.
* **VoxEngine → Line Agent configuration**: pass telephony context and callback endpoints to Line using the `metadata` object in `client.start({ ... })` so the agent can request out-of-band actions from VoxEngine.
* **Barge-in and turn-taking**: interruption behavior between caller/callee and the agent is managed by the Line Agent runtime; no additional VAD or turn-taking configuration is required in VoxEngine.
* **Telephony tools for Voximplant-controlled routing**: Line built-ins like `end_call` and `transfer_call` are designed for Line-native calling flows. For Voximplant-owned flows (warm transfer, SIP handoff, post-call survey), define passthrough tools in Line that signal VoxEngine out-of-band, then execute the telephony action in VoxEngine.

The [Function Calling example](cartesia-line-agents-voice-ai-example-function-calling) demonstrates how to use the HTTP callback pattern for Line → VoxEngine control.
See the [Cartesia module API reference](https://voximplant.com/docs/references/voxengine/cartesia) for all methods and events.

## Examples

* [Example: Answering an incoming call](cartesia-line-agents-voice-ai-example-answering-incoming-call)
* [Example: Placing an outbound call](cartesia-line-agents-voice-ai-example-placing-outbound-call)
* [Example: Function calling](cartesia-line-agents-voice-ai-example-function-calling)

## Links

### Voximplant

* Cartesia Line Agents client product page: [https://voximplant.com/products/cartesia-agents-client](https://voximplant.com/products/cartesia-agents-client)
* Cartesia module API reference: [https://voximplant.com/docs/references/voxengine/cartesia](https://voximplant.com/docs/references/voxengine/cartesia)
* Voice AI product overview: [https://voximplant.ai/](https://voximplant.ai/)

### Cartesia

* Cartesia Line docs: [https://docs.cartesia.ai/line](https://docs.cartesia.ai/line)
* Cartesia CLI deployment: [https://docs.cartesia.ai/line/cli](https://docs.cartesia.ai/line/cli)
* Web calls integration: [https://docs.cartesia.ai/line/integrations/web-calls](https://docs.cartesia.ai/line/integrations/web-calls)