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

# Add Backchannel

> Enable your UponAI agent to make natural listening sounds like 'uh-huh' and 'I see' during caller speech.

Backchannel lets the agent make small acknowledgment sounds — like "uh-huh", "I see", or "okay" — while the caller is speaking. This improves engagement and makes the conversation feel more natural.

## Configuration Fields

Set these fields via the Create Agent API or your agent settings:

**`enable_backchannel`**
Set to `true` to enable backchannel. Defaults to `false`.

**`backchannel_frequency`**
Controls how often backchannel triggers when the engine determines a backchannel is appropriate. Range: `0` (never) to `1` (always). Default: `0.8`.

**`backchannel_words`**
The words the agent can use as backchannels. Defaults vary by language and voice provider. You can override this field to customize the words used.

<Note>
  Certain voices do not work well with certain words. Experiment before customizing the word list.
</Note>

## Default Backchannel Words by Provider

<Tabs>
  <Tab title="English (en)">
    | Voice provider | Default words                           |
    | -------------- | --------------------------------------- |
    | ElevenLabs     | `"okay"`, `"uh-huh"`, `"mhmm"`, `"yah"` |
    | OpenAI         | `"okay"`, `"uh-huh"`, `"yah"`           |
    | Deepgram       | `"okay"`, `"uh-huh"`, `"yah"`           |
  </Tab>

  <Tab title="Other languages">
    Defaults for Spanish (es), Hindi (hi), German (de), French (fr), Japanese (ja), and Portuguese (pt) are set automatically based on language and voice provider support.
  </Tab>
</Tabs>