Skip to main content
Add custom function tool interface in Bolna Voice AI Playground showing function integration options for enhanced agent capabilities

Add a Custom Function Tool with Bolna Voice AI Agents in Playground


You can design your own functions and use them in Bolna. Custom functions follow the OpenAI specifications. You can paste your valid JSON schema and define your own custom function.
Custom function call configuration screen in Bolna Voice AI showing schema input for adding your custom tool with Voice agent

Screenshot of custom function call integration in Bolna Voice AI


​
Steps to write your own custom function

  • Make sure the key is set as custom_task.
  • Write a good description for the function. This helps the model to intelligently decide to call the mentioned functions.
  • All parameter properties must be mentioned in the value param as a JSON and follow Python format specifiers like below
ParamTypeVariable
user_namestr%(user_name)s
user_ageint%(user_age)i
costfloat%(cost)%f

​
More examples of writing custom function calls

curl
--location 'https://my-api-dev.xyz?customer_phone=+19876543210' \
--header 'Authorization: Bearer ***' \
--header 'header1: value1' \
--header 'header2: value2'
The above request corresponds to the following GET custom function:
{
  "name": "get_product_details",
  "description": "Use this tool to fetch product details",
  "parameters": {
    "type": "object",
    "properties": {
      "customer_phone": {
        "type": "string",
        "description": "This is customer's phone number"
      }
    }
  },
  "key": "custom_task",
  "value": {
    "method": "GET",
    "param": {
      "customer_phone": "%(customer_phone)s"
    },
    "url": "https://my-api-dev.xyz",
    "api_token": 'Bearer ***',
    "headers": {
      "header1": "value1",
      "header2": "value2"
    }
  }
}

curl --location 'https://my-api-dev.xyz/v1/store_rating' \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer ***' \
--header 'version: 1.0' \
--data '{
    "customer_id": "134532",
    "rating": "2.3"
}'
The above request corresponds to the following POST custom function:
{
  "name": "save_feedback",
  "description": "Use this tool to save customer's feedback",
  "parameters": {
    "type": "object",
    "properties": {
      "customer_id": {
        "type": "string",
        "description": "This is customer's ID"
      },
      "rating": {
        "type": "string",
        "description": "This is the rating provided by the customer"
      }
    }
  },
  "key": "custom_task",
  "value": {
    "method": "POST",
    "param": {
      "customer_id": "%(customer_id)s"
      "rating": "%(rating)s"
    },
    "url": "https://my-api-dev.xyz/v1/store_rating",
    "api_token": 'Bearer ***',
    "headers": {
      "version": "1.0"
    }
  }
}

​
Using variables and dynamic context

All variables that are part of the agent prompt if included in custom function will be substituted automatically with their appropriate values. The model won’t enquire for these values since they’re already available. You can check the following demonstration. 

This is your agent Sam and you're speaking to {customer_name}.
Please have a frienly conversation with the customer.

Please note:
The agent has a unique id which is "{agent_id}".
The call's unique id is "{call_sid}".
The customer's phone number is "{to_number}".

​
Next steps

Ready to implement custom functions in your voice AI agents? Configure your functions in the Playground Functions tab or use the Agent API for programmatic integration. For related capabilities:
⌘I