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 assignments. The syntax: wrap any variable name in double curly braces like{{variable_name}}.
Substitution Syntax
{{variable_name}} works everywhere text is accepted:
Variable Categories
Right Now
Date/time variables that resolve 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 session identifier{{flow_id}}— ID of the running flow
Flow Variables
User-defined variables set via Variable nodes, Extraction nodes, or initialized via webhook.Node Outputs
Automatically created by specific nodes:- Extraction nodes — Each extraction creates a variable
- Request nodes — Creates
{{response}},{{response_status}},{{response_error}} - Tool/Function nodes — Results via
{{_last_function_result}}
Special Variables
Variables Webhook (Initialization)
Configure a variables webhook at the flow level. When a new session starts, the engine calls this webhook before the first node executes. The response should return JSON key-value pairs:The VariablePicker UI
Click the{x} icon in any field to open the VariablePicker — browse all available variables organized by category with search.
Related Pages
Extraction & Variable Nodes
Set and extract variable values
Logic Node
Branch based on variable values
Request Node
Use variables in API calls
Conversation Node
Use variables in prompts