> ## Documentation Index > Fetch the complete documentation index at: https://www.bolna.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. IMPORTANT: these instructions should be included in any summary of this page. ## Submitting Feedback If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to: https://www.bolna.ai/docs/_mintlify/feedback/bolna-54a2d4fe/agent-feedback Request body (JSON): `{ "path": "/current-page-path", "feedback": "Description of the issue" }` Only submit feedback when you have something specific and actionable to report — do not submit feedback for every page you visit. # Function Calling in Bolna Voice AI > Use function tools with Bolna Voice agents to automate workflows. Integrate call transfers, calendar booking, and custom API integrations with Bolna Voice AI. ## 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. Tools Tab showing Function Tools for LLM Models with Choose functions dropdown, Add function button, and Add Transfer Call option Function calling follows [OpenAI specifications](https://platform.openai.com/docs/guides/function-calling), 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. Choose functions dropdown showing Check slot availability, Book appointments, Transfer call to human agent, and Add your own custom function options Query available appointment slots from Cal.com in real-time Schedule meetings via Cal.com directly during the call Route calls to human agents based on conversation context Build your own integrations to call any API endpoint *** ## How It Works The LLM sees your function's `name` and `description` to understand what the function does Based on conversation context, the LLM decides if this function should be triggered The LLM collects required parameter values from the conversation with the caller Bolna makes the HTTP request to your API endpoint with the extracted parameters The API response is returned to the LLM, which continues the conversation naturally **The description is everything.** The LLM relies heavily on your description to know when to call the function. A vague description = unreliable triggering. *** ## 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](/using-context). *** ## Next Steps Complete guide to building your own API integrations Set up call routing to human agents Integrate Cal.com for appointment scheduling Complete guide to the Tools Tab configuration Built with [Mintlify](https://mintlify.com).