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Variable syntax diagram You can use template variables in both headers and body for HTTP endpoints. Template format: 
{{var_type.var_name}}
For LLM variables, include a description: 
{{llm.var_name:description}}
Templates and variables diagram

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Secret variables

Syntax: 
{{secret.var_name}}
Use this for sensitive values such as API keys, tokens, and tenant secrets. secret variables must be created in akapulu.com/secrets.
Secret variables are allowed only in endpoint headers (function tools and pre_actions/post_actions). Secret variables are not allowed in request body fields, role_messages, or task_messages. In custom UI implementations, HTTP tool-call activity is emitted to the frontend via RTVI server-message events and includes the full request body payload. See Customize Conversation UI.
Examples: 
{
  "headers": {
    "Authorization": "Bearer {{secret.crm_api_key}}",
    "X-Tenant-Token": "{{secret.tenant_token}}"
  },
  "body": {
    "source": "akapulu_assistant"
  }
}

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Runtime variables

Syntax: 
{{runtime.var_name}}
Use this for per-session values that your app passes at connect time (for example user IDs, session IDs, org IDs). runtime variables must be passed to the connect endpoint as runtime_vars. Examples: 
{
  "headers": {
    "X-Session-ID": "{{runtime.session_id}}"
  },
  "body": {
    "patient_id": "{{runtime.patient_id}}",
    "workspace_id": "{{runtime.workspace_id}}"
  }
}

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LLM variables

Syntax: 
{{llm.var_name:description}}
Use this for dynamic values the model should fill at tool-call time. The description is shown to the model as part of normal tool-call parameter guidance, so write it clearly and specifically. Examples: 
{
  "body": {
    "date": "{{llm.date:Appointment date in YYYY-MM-DD format}}",
    "time": "{{llm.time:Appointment time in HH:MM 24-hour format}}",
    "reason": "{{llm.reason:Short reason for visit from user request}}"
  }
}

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Function tools vs pre/post actions

{{llm.*}} variables are only supported for HTTP endpoints configured as function tools. They are not supported in HTTP endpoints configured as pre_actions or post_actions, because those endpoints run automatically without an LLM tool call.

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Function tools (LLM-available)

The LLM can call these tools and fill {{llm.*}} variables. Akapulu syntax for functions

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Pre-actions and post-actions (automatic)

These run automatically on node lifecycle and are not called by the LLM. Akapulu syntax for pre/post actions

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Mixed example

You can combine all variable types in one endpoint: 
{
  "headers": {
    "Authorization": "Bearer {{secret.crm_api_key}}",
    "X-Session-ID": "{{runtime.session_id}}"
  },
  "body": {
    "patient_id": "patient_{{runtime.patient_id}}",
    "appointment_date": "{{llm.date:Appointment date in YYYY-MM-DD format}}",
    "appointment_time": "{{llm.time:Appointment time in HH:MM 24-hour format}}"
  }
}
Example actual request (after variable resolution): 
{
  "headers": {
    "Authorization": "Bearer sk_live_abc123",
    "X-Session-ID": "sess_9f2a1c"
  },
  "body": {
    "patient_id": "patient_2938573456",
    "appointment_date": "2026-03-18",
    "appointment_time": "14:00"
  }
}