Automated Voice Appointment Booking with Vapi AI and Google Calendar

What this template does

Connect a Vapi AI voice agent to Google Calendar to capture contact details and auto-book appointments.
The agent asks for name, address, service type, and a preferred time. The workflow checks availability and either proposes times or books the slot—no code needed.

How it works (node map)

• Webhook: Production URL = VAPI Server URL — receives tool calls from Vapi and returns results.
• 1. CONFIGURATION (EDIT ME) — your timezone, work hours, meeting length, buffers, and cadence.
• Route by Tool Name — routes Vapi tool calls:
  • checkAvailability → calendar lookup path
  • bookAppointment → create event path
• 2. Get Calendar Events (EDIT ME) — reads events for the requested day.
• Calculate Potential Slots / Filter for Available Slots — builds conflict-free options with buffers.
• Respond with Available Times — returns formatted slots to Vapi.
• 3. Book Appointment in Calendar (EDIT ME) — creates the calendar event with details.
• Booking Confirmation — returns success back to Vapi.

Sticky notes in the canvas show exactly what to edit (required by n8n).
No API keys are hardcoded; Google uses OAuth credentials.

Requirements

• n8n (Cloud or self-hosted)
• Google account with Calendar (OAuth credential in n8n)
• Vapi account + one Assistant

Setup (5 minutes)

A) Vapi → n8n connection

1. Open the Webhook node and copy the Production URL.
2. In Vapi → Assistant → Messaging , set Server URL = that Production URL.
3. In Server Messages , enable only toolCalls.

B) Vapi tools (names must match exactly)

Create two Custom Tools in Vapi and attach them to the assistant:

Tool 1: checkAvailability

• Arguments
  • initialSearchDateTime (string, ISO-8601 with timezone offset, e.g. 2025-09-09T09:00:00-05:00)

Tool 2: bookAppointment

• Arguments
  • startDateTime (string, ISO-8601 with tz)
  • endDateTime (string, ISO-8601 with tz)
  • clientName (string)
  • propertyAddress (string)
  • serviceType (string)

The Switch node routes based on message.toolCalls[0].function.name. If the names differ, nothing will run.

C) Configure availability

Open 1. CONFIGURATION (EDIT ME) and set:

• timeZone (e.g. America/New_York)
• workdayStartHour / workdayEndHour (24h integers)
• meetingDurationMinutes (e.g. 30 or 60)
• bufferBeforeMinutes / bufferAfterMinutes (e.g. 15)
• bookingCadenceMinutes (e.g. 30)

D) Connect Google Calendar

1. Open 2. Get Calendar Events (EDIT ME) → Credentials: select/create Google Calendar OAuth.
   Then choose the calendar to check availability.
2. Open 3. Book Appointment in Calendar (EDIT ME) → use the same credential and same calendar to book.

E) Activate & test

• Toggle the workflow Active.
• Call your Vapi number (or start a session) and book a test slot.
• Verify the event appears with description fields (client, address, service type, call id).

Customising

• Change summary/description format in 3. Book Appointment.
• Add SMS/Email confirmations, CRM sync, rescheduling, or analytics as follow-ups (see sticky note “I’m a note”).

Troubleshooting

• No response back to Vapi → confirm Vapi is set to send toolCalls only and the Server URL matches the Production URL.
• Switch doesn’t route → tool names must be exactly checkAvailability and bookAppointment.
• No times returned → ensure timezone + work hours + cadence generate at least one future slot; confirm Google credential and calendar selection.
• Event not created → use the same Google credential & calendar in both nodes; check OAuth scopes/consent.

Security & privacy

• Google uses OAuth; credentials live in n8n.
• No API keys hardcoded.
• Webhook receives only the fields needed to check times or book.