What is Function Calling? (Tools / tool use)
2 min read · Bolcho
Function calling (or tool calling) is the mechanism that lets a voice agent take real actions instead of just talking. The language model decides when to call a defined function — like book_appointment or send_payment_link — with the right arguments, and uses the result to continue the conversation.
Function Calling explained
You define a set of tools with names, descriptions and parameters. Mid-conversation, the model recognises 'book me for 4pm tomorrow' and calls book_appointment(date, time) with the parsed values, then confirms based on what the tool returns.
This is what turns a chatbot into an agent: it can check availability, create records, send messages and transfer calls — grounded in your real systems.
How it works
The model is given tool schemas. When the conversation needs one, it emits a structured call; your backend runs it and returns a result; the model reads the result and speaks the next line. It can chain several calls in one conversation.
How Bolcho handles it
Bolcho ships function calling with native tools for the actions Indian businesses need.
Tools that take action
Out of the box, agents can book slots, look up orders, transfer to a human, and send a mid-call Razorpay payment link over SMS/WhatsApp — plus your own custom API tools.
Why it matters for voice AI in India
The highest-value Indian use cases — COD confirmation with a UPI link, site-visit booking, appointment scheduling — are all function calls. Having payments and messaging as first-class tools is what makes them one-step.
See it in a real agent
Bolcho handles this for you end-to-end. Start a voice or chat agent free.
Frequently asked questions
What is function calling?
It's how a voice agent invokes your defined tools (functions) mid-conversation — like booking a slot or sending a payment link — using the language model to pick the right function and arguments.
What can a Bolcho agent do with tools?
Book appointments, look up orders, transfer to a human, and send a Razorpay payment link over SMS/WhatsApp on the call — plus any custom API tools you define.
Is function calling the same as an agent?
It's the core capability that makes an agent 'agentic' — able to take actions in your systems, not just converse.