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What is book calendar slots?

The Book Calendar Slots function allows your Voice AI agent to schedule appointments directly into your Cal.com calendar during live conversations. After a caller selects a time slot, your agent can book it instantly.
Cal.com configuration modal for book_appointment with a Task Name field, a Description (Prompt) box, a Pre-tool message with an English language tab and an Add button, an API key (Cal.com) field and disabled Select Events and Choose Timezone dropdowns

Cal.com configuration for book_appointment

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Configuration options

Select Events and Choose Timezone dropdowns appear only after entering a valid Cal.com API key.

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How to set up

1

Open Tools Tab

Navigate to Tools Tab in your agent configuration.
2

Add Book Appointment

Find Book Appointment in the tool catalog and click Add.
3

Enter API Key

Paste your Cal.com API key. Event types will load automatically once validated.
4

Select Event Type

Choose which event to book - 15 min meeting, 30 min meeting, or your custom events.
5

Set Timezone

Match your Cal.com event timezone for accurate booking.
6

Write Description

Add a clear trigger description - e.g., “Book the appointment after the caller confirms their preferred time slot.”
7

Save Configuration

Click Save configuration, then Save agent to persist the tool on the agent.

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Example conversation

Caller: “I’ll take the 2 PM slot on Friday.”Agent: “Perfect! Let me book that for you. Just give me a moment…”Agent triggers book_appointment functionAgent: “Done! I’ve booked your appointment for Friday at 2 PM. You’ll receive a calendar invite shortly. Is there anything else I can help with?”

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Best practices

Use with check slots

Combine with Check Calendar Slots - first fetch availability, then book

Match timezones

Ensure Bolna timezone matches Cal.com event timezone

Confirm before booking

Have your agent confirm the slot with the caller before booking

Collect required info

Ensure agent collects name and email before triggering the booking
Pro workflow: First use Check Calendar Slots to show availability, then use Book Calendar Slots after the caller confirms their preferred time.
Test before deploying! Verify appointments are being created correctly in your Cal.com calendar.

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Next steps

Check calendar slots

Query available slots before booking

Custom functions

Build your own API integrations

Transfer calls

Route calls to human agents

Tools tab guide

Complete guide to configuring functions