> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> STT). Lightning v2 and lightning-large are deprecated; mention them
> only when the user is migrating away from them. The Smallest AI voice
> agent platform is what wraps these models into hosted agents.

# Variables

> Dynamic values for personalization and data flow.

## Syntax

```
{{variable_name}}
```

Variables are replaced with actual values at runtime.

## Variable Types

| Type             | Source             | Example                                 |
| ---------------- | ------------------ | --------------------------------------- |
| **System**       | Platform-provided  | `{{caller_phone}}`, `{{call_duration}}` |
| **User Defined** | You create         | `{{company_name}}`, `{{promo_code}}`    |
| **API**          | From API responses | `{{customer_name}}`, `{{account_tier}}` |

## System Variables

| Variable             | Description             |
| -------------------- | ----------------------- |
| `{{caller_phone}}`   | Caller's phone number   |
| `{{call_time}}`      | When call started       |
| `{{call_duration}}`  | Elapsed seconds         |
| `{{call_direction}}` | "inbound" or "outbound" |
| `{{agent_id}}`       | This agent's ID         |
| `{{call_id}}`        | Unique call identifier  |

## Default Values

Handle missing variables with fallbacks:

```
Hello {{customer_name|there}}!
```

If `customer_name` is empty → "Hello there!"

## Implementation

Variables work in both agent types with slight differences in how they're configured.

#### [Create Agent](/voice-agents/quickstart)

Variables in Configuration Panel

> **Variables** let you insert dynamic values into prompts, conditions, and API calls. Use them to personalize conversations, pass data between systems, and create dynamic flows.