Variables & Dynamic Data

Overview

Variables are the data layer of Flow Builder. They let you store, transform, and inject dynamic values throughout your flow — in prompts, URLs, headers, request bodies, and variable assignments. The syntax is simple: wrap any variable name in double curly braces like {{variable_name}}.

Substitution Syntax

The {{variable_name}} syntax works everywhere text is accepted:

Where	Example
Conversation prompts	You are speaking with {{caller_name}}
Request URLs	https://api.example.com/users/{{user_id}}
Request headers	Authorization: Bearer {{api_token}}
Request body	{"email": "{{email}}", "name": "{{full_name}}"}
Variable assignments	{{first_name}} {{last_name}}
Query parameters	filter={{status}}&limit=10

At runtime, the engine replaces each {{variable}} with its current value before the node executes.

Variable Categories

Variables are organized into four categories in the VariablePicker UI:

Right Now

Date and time variables that resolve to the current moment at runtime:

• {{current_date}} — Today's date
• {{current_time}} — Current time
• {{current_day}} — Day of the week

System

Session-level variables populated automatically:

• {{session_key}} — Unique identifier for the current session
• {{flow_id}} — ID of the running flow

Flow Variables

User-defined variables set via Variable nodes, Extraction nodes, or initialized via webhook. These are the variables you create and control.

Node Outputs

Variables automatically created by specific node types:

• Extraction nodes — Each extraction creates a variable with the extracted value
• Request nodes — Creates {{responseVariable}}, {{responseVariable_status}}, and {{responseVariable_error}}
• Tool/Function nodes — Results accessible via {{_last_function_result}}

The VariablePicker UI

When editing any field that supports variables, click the variable icon ({x}) to open the VariablePicker. It shows all available variables organized by category, with a search bar to quickly find what you need. Click a variable to insert it at the cursor position.

Special Variables

Variable	Description
{{_last_function_result}}	The return value of the most recently executed Tool/Function node
{{response_status}}	HTTP status code from the last Request node (if using a generic name)
{{responseVariable_status}}	HTTP status code from a specific Request node's response
{{responseVariable_error}}	Error message from a specific Request node if it failed

Variables Webhook (Initialization)

You can configure a variables webhook at the flow level. When a new session starts, the engine calls this webhook before the first node executes. The webhook response should return a JSON object of key-value pairs — each pair becomes a flow variable.

This is how you pre-load caller data, account information, or configuration into the flow at the start of every conversation:

// Webhook response example
{
  "caller_name": "Sarah Johnson",
  "account_id": "ACC-4821",
  "plan": "premium",
  "language": "English"
}

These variables are immediately available in your start node's prompt and throughout the flow.

Tip: Use the variables webhook to pass caller ID, CRM data, or session context into your flow. This lets the AI greet callers by name and skip data collection steps.