Variables

Overview

Use dynamic variables in the system prompt or any message in the dashboard with double curly braces (e.g., {{name}}).

To set values, make a phone call request through the API and set assistantOverrides. You cannot set variable values directly in the dashboard.

For example, set the assistant’s first message to “Hello, {{name}}!” and assign name to John by passing assistantOverrides with variableValues:

1
{
2
  "variableValues": {
3
    "name": "John"
4
  }
5
}

Using dynamic variables in a phone call

1
{
2
  "assistantId": "your-assistant-id",
3
  "assistantOverrides": {
4
    "variableValues": {
5
      "name": "John"
6
    }
7
  },
8
  "customer": {
9
    "number": "+1xxxxxxxxxx"
10
  },
11
  "phoneNumberId": "your-phone-id"
12
}

Default Variables

These variables are automatically filled based on the current (UTC) time, so you don’t need to set them manually in variableValues:

Advanced date and time usage

You can use advanced date and time formatting in any prompt or message that supports dynamic variables in the dashboard or API. We use LiquidJS for formatting - see their docs for details.

Format a date or time using the LiquidJS date filter:

1
{{"now" | date: "%A, %B %d, %Y, %I:%M %p", "America/Los_Angeles"}}

Outputs: Monday, January 01, 2024, 03:45 PM

Examples:

• 24-hour time:

  1
  {{"now" | date: "%H:%M", "Europe/London"}}
  → 17:30
• Day of week:

  1
  {{"now" | date: "%A"}}
  → Tuesday
• With customer number:

  1
  Hello, your number is {{customer.number}} and the time is {{"now" | date: "%I:%M %p", "America/New_York"}}

Common formats:

Using dynamic variables in the dashboard

To use dynamic variables in the dashboard, include them in your prompts or messages using double curly braces. For example:

1
Hello, {{name}}!

When you start a call, you must provide a value for each variable (like name) in the call configuration or via the API/SDK.

Setting assistant prompt using conversation type

Using the transport.conversationType variable in your assistant’s system prompt, you can modify how it behaves in chats or calls:

1
[Identity]
2
You are a helpful assistant, talking with a customer via {{transport.conversationType}}.
3
4
[Response Guidelines]
5
{% if transport.conversationType == "chat" -%}
6
- Format numbers naturally; eg, a US phone number could be +1 (555) 123-4567
7
- Use Markdown formatting for lists (both unordered and ordered)
8
{%- elsif transport.conversationType == "voice" -%}
9
- Always spell numbers in words; eg, 256 should be 'two hundred and fifty six'
10
- Only ask one question at a time
11
- Never use Markdown format; write everything as if it is being said aloud
12
{%- endif -%}

HIPAA and Zero Data Retention mode

When HIPAA mode or Zero Data Retention is enabled for your organization or assistant, Vapi does not store any call data, including variable values. This means:

• Variable values passed via variableValues are processed during the call but not persisted after the call ends
• Call logs, recordings, and transcriptions are not stored
• Variables are only available in real-time during the active call session

This ensures compliance with privacy requirements while still allowing you to personalize conversations with dynamic variables.