Google Calendar Free/Busy Auto-Responder

Overview

FlowLibs - Google Calendar Free Busy Auto-Responder is an automated cloud flow that watches a mailbox for incoming meeting-request emails, queries Google Calendar for upcoming busy time blocks, and replies to the sender with a formatted HTML schedule so they can pick a free slot.

The flow ships Off as a reference implementation. Turning it on requires only authorizing the Office 365 Outlook and Google Calendar connections and (optionally) tuning the four environment variables.

Use Case

When you publish a calendar booking link or accept meeting requests via email, the back-and-forth of "what time works for you?" creates inbox friction. This flow auto-acknowledges every meeting-request email with your live calendar so the sender can self-serve a free slot on the first round-trip — no scheduling tools, no shared availability page, no manual lookup.

The flow is ideal for teams that:

• Sales reps
• Customer success managers
• Founders running their own scheduling
• Anyone whose Google Calendar is the single source of truth for availability

Flow Architecture

Environment Variables

Connectors & Connections

Note — All connections are referenced as solution connection references; the flow is portable between environments as long as a connection is mapped at import time.

Customization Guide

Almost every realistic variant of this flow can be implemented by changing environment variable values. A few cases require small edits inside the flow definition — those are called out explicitly below.

Re-target the calendar

Set flowlibs_GoogleCalendarId to any calendar ID the connected Google account can see (an email like team@yourcompany.com, a shared-calendar ID, or 'primary').

Change the trigger phrase

Update flowlibs_AutoResponderTriggerSubject to whatever subject substring should fire the auto-response (e.g. 'schedule a call', 'book time', '15 mins'). The OnNewEmailV3 subjectFilter parameter is bound to this env var via @parameters('flowlibs_AutoResponderTriggerSubject'), so the change takes effect on the next polling cycle.

Widen / narrow the lookahead

Change flowlibs_FreeBusyLookaheadDays to control how many days ahead are returned. Values are strings in the env var (Power Platform constraint) and cast to int at flow-runtime via @int(parameters('flowlibs_FreeBusyLookaheadDays')).

Filter to working hours / business days

Add a Filter Array action between List Calendar Events and Init varBusyHtml keyed off dayOfWeek(item()?['start']?['dateTime']) and formatDateTime(...,'HH') to drop weekends / nights from the rendered table.

Switch from busy-times to true free-slots

Replace the foreach with a range(0, varLookaheadDays) walker that builds candidate hour blocks and filters out any that overlap an event in body('List_Calendar_Events')?['items'].

Move to a shared mailbox

Replace the trigger with SharedMailboxOnNewEmailV2 and add a mailboxAddress parameter — the rest of the flow is unchanged because triggerOutputs()?['body/from'] and body/subject remain in the same shape.

Send via Outlook.com instead of Office 365

Swap the two Outlook actions for shared_outlook equivalents and re-author the trigger output references to PascalCase (body/From, body/Subject) per the connector's schema.

Key Expressions

The flow is intentionally light on Power Fx / WDL gymnastics — the heaviest expressions are the branch-name concatenation and the approval outcome check. They are listed below in the order they appear in the flow.

@parameters('flowlibs_AutoResponderTriggerSubject')

@int(parameters('flowlibs_FreeBusyLookaheadDays'))

@{formatDateTime(utcNow(), 'yyyy-MM-ddTHH:mm:ss.fffZ')}

@{formatDateTime(addDays(utcNow(), variables('varLookaheadDays')), 'yyyy-MM-ddTHH:mm:ss.fffZ')}

coalesce(items('For_Each_Calendar_Event')?['start']?['dateTime'], items('For_Each_Calendar_Event')?['start']?['date'])

@triggerOutputs()?['body/from']

@{concat('Re: ', triggerOutputs()?['body/subject'])}