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Variable availability depends on agent type and flow position. The system uses flow analysis to decide which variables each node (or single prompt) can use.

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Availability by Variable Type

Variable TypeGlobal NodesRegular NodesSingle-Prompt AgentLogic
System Variables✅ Yes✅ Yes✅ YesAlways available
Custom Variables✅ Yes✅ Yes✅ YesAlways available
Extracted Variables❌ No✅ Yes*❌ NoOnly from predecessor nodes
Static Variables❌ No✅ Yes*❌ NoOnly from predecessor nodes
* Only if the current node runs after the node that created the variable.

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Flow Position Rules (Flow Agent)

  1. Predecessors only: A node sees variables only from nodes that run before it.
  2. Execution paths: All possible paths are considered when computing predecessors.
  3. Global nodes: Nodes with isGlobal: true see only system and custom variables.
  4. Caching: Availability is cached per node and refreshed when the flow changes.

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Example Flow

Start Node (creates: user_phone)
  ↓
Conversation Node (creates: customer_name, appointment_date)
  ↓
Tool Node (creates: booking_id, confirmation_code)
  ↓
End Node

Available at each step:
- Start Node: system, custom
- Conversation Node: system, custom, user_phone
- Tool Node: system, custom, user_phone, customer_name, appointment_date
- End Node: system, custom, user_phone, customer_name, appointment_date, booking_id, confirmation_code

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Single Prompt Agent Variables

Single prompt agents are standalone conversational agents that don’t use the flow builder. They have a simplified variable model optimized for quick deployment and simple use cases.

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Variable Availability

Variable TypeAvailableNotes
System Variables✅ YesAll 15+ platform variables available
Custom Variables✅ YesConverted to params in configuration
Extracted Variables❌ NoNo flow nodes to extract from
Static Variables❌ NoNo nodes to define static variables

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How Custom Variables Work in Single Prompt Agents

Custom variables in single prompt agents act as parameters that configure the agent: Definition (Variables Panel): 
Custom Variables:
- business_name: "Acme Corporation"
- support_email: "[email protected]"
- max_conversation_turns: 10
- enable_transfers: true
Conversion to params: 
// Custom variables become params in agent configuration
{
  params: {
    business_name: "Acme Corporation",
    support_email: "[email protected]",
    max_conversation_turns: 10,
    enable_transfers: true
  }
}
Usage in prompt: 
You are a customer service agent for {{business_name}}.
If customers need help, direct them to {{support_email}}.
Keep conversations under {{max_conversation_turns}} turns.
{{#if enable_transfers}}You can transfer calls to human agents.{{/if}}

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Key Differences from Flow Builder Agents

AspectFlow Builder AgentsSingle Prompt Agents
ComplexityMulti-node workflowsSingle prompt configuration
VariablesSystem + Custom + Extracted + StaticSystem + Custom only
ExtractionAI extraction, toolpath, DTMFNot supported
Flow LogicConditional branching, loopsLinear conversation
Custom VariablesWorkflow-level stateConfiguration parameters
Use CaseComplex workflowsSimple conversational agents

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Use Cases for Single Prompt Agents

Good for:
  • Simple Q&A agents
  • Information lookup agents
  • Basic customer service
  • FAQ bots
  • Quick prototypes
  • Agents with minimal state
Not good for:
  • Multi-step workflows
  • Data collection and processing
  • API integrations with variable extraction
  • Complex conditional logic
  • State management across multiple steps

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Configuration Example

Variables Panel (Custom Variables): 
agent_name: "SupportBot"
company_name: "TechCorp"
working_hours: "9 AM - 5 PM EST"
escalation_enabled: true
Single Prompt Configuration: 
System Prompt:
You are {{agent_name}}, a helpful assistant for {{company_name}}.
Our working hours are {{working_hours}}.
Current time: {{current_time}}
Current date: {{current_date}}

Instructions:
- Be friendly and professional
- Answer questions about our products
{{#if escalation_enabled}}
- Offer to escalate complex issues to human agents
{{/if}}

User's phone: {{user_number}}
Call direction: {{direction}}
Available variables in this example:
  • ✅ agent_name, company_name, working_hours, escalation_enabled (custom)
  • ✅ current_time, current_date, user_number, direction (system)

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When to Upgrade to Flow Builder

Consider upgrading to a Flow Builder agent when you need to:
  • Extract data from conversations (AI extraction)
  • Integrate with APIs and parse responses (toolpath extraction)
  • Use conditional branching or multi-step logic
  • Collect structured information across nodes
  • Use DTMF capture or static variables
For DOs and DON’Ts specific to single prompt agents, see Best Practices: Single Prompt Agent Variables.

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Variable Categories & Display

Variables are grouped for the UI:
CategoryIconContains
System🔧Platform variables
Custom⚙️Workflow-level variables
Extracted📤From nodes (AI, toolpath, DTMF)
Static📌Node-level set values
Displayed per variable: name, type, source (for extracted/static), description, default/example value.

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Context-Aware Recommendations

The UI can suggest variables based on node type and content:
  • Conversation: e.g. customer_name, phone_number, appointment_date, issue_description
  • Tool: e.g. api_response, status_code, response_data, error_message
  • Transfer: e.g. transfer_reason, customer_context, conversation_summary
See UI Components & Validation for where these appear and Introduction for the overall model.