***

title: Variables
sidebarTitle: Variables
description: Use dynamic values throughout your conversation flow.
------------------------------------------------------------------

Variables let you personalize conversations with dynamic data — caller information, API responses, or values you define.

**Location:** Workflow tab → **{ } Variables** button (top right)

<Frame caption="Variables panel">
  ![Variables panel](https://files.buildwithfern.com/smallest-ai.docs.buildwithfern.com/64924894de4d6991223c171a8ec3e3155efad27b1e74b8deefff34763bb03e82/products/atoms/pages/platform/building-agents/images/cf-variables-panel.png)
</Frame>

***

## Variable Types

| Type             | Source                        | Example                                 |
| ---------------- | ----------------------------- | --------------------------------------- |
| **User Defined** | Variables you create          | `{{company_name}}`, `{{promo_code}}`    |
| **System**       | Platform-provided (read-only) | `{{caller_phone}}`, `{{call_duration}}` |
| **API**          | Extracted from API responses  | `{{customer_name}}`, `{{account_tier}}` |

***

## Syntax

Use double curly braces anywhere in prompts or conditions:

```
Hello {{customer_name}}! Thanks for calling {{company_name}}.
```

### Default Values

Handle missing variables with the pipe syntax:

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

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

***

## 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  |

***

## Creating Variables

1. Click **{ } Variables** in the workflow tab
2. Go to **User Defined** tab
3. Click **+ Add Variable**
4. Enter name and default value

***

## Extracting from APIs

In API nodes, use **Extract Response Data** to create variables from responses:

| JSONPath      | Variable        |
| ------------- | --------------- |
| `$.data.name` | `customer_name` |
| `$.data.tier` | `account_tier`  |