What is Function Calling?
Function calling enables your Voice AI agents to execute real-time actions during live conversations. Instead of just responding with text, your agent can transfer calls, book appointments, fetch data from APIs, or trigger any custom workflow.
Function calling follows OpenAI specifications, so you can use existing function schemas with Bolna.
Built-in Function Tools
Bolna provides ready-to-use tools for common use cases. Select them from the “Choose functions” dropdown - no coding required.
Check Slot Availability
Query available appointment slots from Cal.com in real-time
Book Appointments
Schedule meetings via Cal.com directly during the call
Transfer Calls
Route calls to human agents based on conversation context
Custom Functions
Build your own integrations to call any API endpoint
How It Works
LLM Reads Function Definition
The LLM sees your function’s
name and description to understand what the function doesDecides When to Call
Based on conversation context, the LLM decides if this function should be triggered
Extracts Parameters
The LLM collects required parameter values from the conversation with the caller
Bolna Executes API Call
Bolna makes the HTTP request to your API endpoint with the extracted parameters
Context Variables
The following variables are available in the conversation context and can be passed to function parameters:| Variable | Description |
|---|---|
{agent_id} | The id of the agent |
{call_sid} | Unique id of the phone call (from Twilio, Plivo, etc.) |
{from_number} | Phone number that initiated the call |
{to_number} | Phone number that received the call |
| Custom variables | Any variable you define in the agent prompt |
Variables defined in your agent prompt are automatically substituted in function parameters. Learn more in Using Context Variables.