# Conversation behavior


# Conversation behavior

The **Engine** tab (labeled **Behavior** in the agent builder) controls how your agent handles the timing and pacing of a live phone call — interruptions, silence and pauses. Set this in the agent builder at **/agent/setup**.

:::note[The prompt and messages are on the Agent tab]

The **system prompt**, the **greeting**, and the **end / fallback / busy / voicemail** messages are configured on the **Agent** tab, not here. This tab is purely about *how* the agent paces a call, not *what* it says. See the [agents overview](./overview).

:::

## Barge-in and interrupts

![The Behavior tab](/img/screenshots/portal/agent-engine.png)
*The Behavior tab: interruption settings (barge-in, stop-TTS-on-interrupt, sensitivity) and silence detection.*

**Barge-in** lets the caller interrupt the agent mid-sentence. Two related controls govern it:

- **Allow barge-in** — whether the caller can interrupt at all.
- **Stop TTS on interrupt** — whether the agent immediately stops speaking when interrupted.
- **Interrupt sensitivity** — how easily an interruption triggers (low / medium / high). Higher sensitivity makes the agent yield quickly, which feels responsive but can trip on background noise; lower sensitivity holds its turn but can feel like it's talking over the caller.

Tune this to your callers' environment.

## Voice-activity-detection padding

The **VAD** settings shape turn-taking by detecting when speech starts and stops:

- **Speech detection padding** (`prefix_padding_ms`) — how much audio before detected speech to keep, so the start of a word isn't clipped.
- **Silence duration** (`silence_duration_ms`) — how long the caller must be silent before the turn is considered complete.

## Response delay

**Response delay** (`response_delay_ms`) inserts a brief pause before the agent replies, so it doesn't jump in the instant the caller stops — a small delay sounds more natural and avoids stepping on a caller who's only pausing.

## Silence handling

These settings decide what the agent does when the caller goes quiet — the **silence timeout**, the **maximum silence duration**, and the **maximum silence count** (how many times the agent re-prompts before ending). Sensible values keep dead air from making the call feel broken without ending it too soon.

## Filler words

Enable **filler words** to let the agent use natural conversational sounds and brief acknowledgements during pauses and turn-taking, and optionally provide your own list. These small touches make the agent feel more human and less robotic.

## Memory and post-call analysis

The Engine tab also exposes a few cross-cutting toggles:

- **Call history memory** — let the agent recall previous calls with the same contact.
- **Auto-summarize** and **sentiment analysis** — opt-in post-call analysis (also surfaced on the Guardrails tab).

:::tip[Hear it, don’t read it]

Pacing only really shows up in voice. Confirm barge-in, silence handling and filler words in the **voice test** at **/agent/interface**, since timing is hard to judge on paper.

:::

## Next steps

- [Set the prompt, greeting and messages on the Agent tab](./overview)
- [Set calling and transfer rules](./calling-telephony)
- [Tune the LLM that drives replies](./llm)
- [Back to the agents overview](./overview)