Webhook Appointment Availability Check for Google Calendar

Instantly check Google Calendar appointment availability via an authenticated Webhook

This n8n workflow exposes a secure webhook that verifies a requested time window and returns a structured JSON response showing whether the slot is available or busy—based on your Google Calendar free/busy data.

What this workflow does

• Receives a POST webhook with authenticated header auth and a JSON body containing start and end timestamps.
• Validates input strictly:
  • Both timestamps must be RFC3339 with seconds and an explicit offset.
  • Start must be in the future.
  • The interval must be positive and no longer than 24 hours.
• Queries Google Calendar for free/busy availability for the provided time window.
• Returns normalized JSON including:
  • status (available or busy)
  • available (boolean)
  • Normalized UTC start and end
• Uses clear HTTP outcomes:
  • 200 for successful checks
  • 400 for validation errors
  • 502 if Google Calendar can’t be queried without making an availability claim

Use cases

• Prevent double-booking in an appointment booking SaaS by checking availability before creating an event.
• Confirm whether a proposed meeting time works when a user selects a slot.
• Integrate n8n into scheduling flows where your app needs a fast webhook-based availability check.

Technical details

• Nodes/tech stack: webhook, if, code, google calendar, respond to webhook (plus supporting workflow notes via sticky note).
• Authentication: Header Auth credential (authenticated webhook).
• Calendar: Google Calendar OAuth, configurable calendar ID.
• Output: Structured JSON availability result.