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. 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 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. 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

Open the Webhook node and copy the Production URL. In Vapi → Assistant → Messaging, set Server URL = that Production URL. 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: 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 C) Configure availability

Open 1. CONFIGURATION (EDIT ME) and set:

D) Connect Google Calendar

Open 2. Get Calendar Events (EDIT ME) → Credentials: select/create Google Calendar OAuth. Then choose the calendar to check availability. 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.