Build a Voice Receptionist for Your Business · 50 min · Vapi · Google Calendar API · Twilio

Tool Integration — Calendar + SMS

A caller waiting on hold for your tool's response doesn't know it's 'just an API call' -- 3 seconds of silence mid-call feels broken regardless of what's happening on your server.

Hiring signal: Real tool-calling from a live voice agent -- with the tighter response-time budget voice imposes -- is a materially harder integration problem than the same tools wired into a text agent, and a genuinely differentiated skill.

What you will learn

Build a webhook server that handles Vapi tool calls
Check real Google Calendar availability and create real events
Send a real SMS confirmation via Twilio after a booking

Introduction

The conversation design knows what to say. Today it can actually do something: check a real calendar, book a real appointment, and text a real confirmation — during a live call, not after it ends.

Vapi tools: your webhook server as the "hands"

Same idea as Course 01's agent tools, higher stakes on timing
Just like Course 01's read_file/web_search tools, a Vapi tool is your own code that Vapi calls when the assistant decides it's needed -- the model can't check a calendar itself, it asks your webhook server to. What's different here: a text agent's tool call can take 5-10 seconds without anyone noticing. A voice agent's tool call happening mid-conversation has the caller sitting in real-time silence, waiting -- Vapi's own guidance is to keep tool responses under roughly 3 seconds for a call to still feel natural.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers Checking real Google Calendar availability, Booking and SMS: the moment the call becomes a real action, What You're Building — plus a hands-on lab, quiz, and project artifact.

Create a free account to unlock Phase 0 and Phase 1 of every course — no credit card.