How to Alert Slack When Google Calendar Room Bookings Conflict with Zapier

Create Zap > Trigger > Google Calendar

Connect Google Calendar to Zapier

First, you'll establish the connection between Zapier and your Google Calendar account. This requires OAuth authentication to access calendar events.

1. 1Click 'Create Zap' from your Zapier dashboard
2. 2Search for 'Google Calendar' in the app selector
3. 3Select 'New or Updated Event' as your trigger
4. 4Click 'Sign in to Google Calendar' and complete OAuth flow

Trigger Setup > Calendar Selection

Select the Room Calendar

Choose which specific calendar contains your room bookings. Zapier will monitor this calendar for any new or changed events that could create conflicts.

1. 1Click the 'Calendar' dropdown in the trigger setup
2. 2Find your room calendar from the list (e.g. 'Conference Room A')
3. 3Leave 'Search Term' blank to monitor all events
4. 4Set 'Time Before' to 1 minute for near real-time detection

Trigger Setup > Test

Test the Google Calendar Trigger

Zapier needs to pull a recent event from your room calendar to understand the data structure. This becomes your sample data for mapping fields later.

1. 1Click 'Test trigger' at the bottom of the setup panel
2. 2Wait for Zapier to fetch recent events (takes 10-15 seconds)
3. 3Review the sample event data that appears
4. 4Click 'Continue with selected record' to proceed

Action > Code by Zapier > Run Python

Add Code by Zapier Step

Since Google Calendar doesn't natively detect conflicts, you need a code step to check if the current event overlaps with existing bookings. This runs Python code to compare timestamps.

1. 1Click the '+' icon to add an action step
2. 2Search for 'Code by Zapier' and select it
3. 3Choose 'Run Python' as the action event
4. 4Skip the account connection (no auth needed for Code steps)

Drop this into a Zapier Code step.

# Add this to your Python code for smarter conflict detection
from datetime import datetime, timedelta
# Only check conflicts in next 7 days

# Add this to your Python code for smarter conflict detection
from datetime import datetime, timedelta

# Only check conflicts in next 7 days
max_check_date = datetime.now() + timedelta(days=7)
event_start = datetime.fromisoformat(input_data['event_start'].replace('Z', '+00:00'))

if event_start > max_check_date:
    return {'conflict_detected': 'false', 'reason': 'event_too_far_future'}

Code Setup > Input Data

Configure Conflict Detection Logic

Set up input variables and Python code that compares the new event's time slot against existing calendar events. The code will return true if an overlap is detected.

1. 1In Input Data, add 'event_start' and map it to 'Start Date Time Pretty' from step 1
2. 2Add 'event_end' and map it to 'End Date Time Pretty' from step 1
3. 3Add 'event_title' and map it to 'Summary' from step 1
4. 4Paste conflict detection code in the Code section

Code Setup > Test & Review

Test the Conflict Detection

Run the Python code with your sample event data to verify it correctly identifies conflicts. The output determines whether Slack gets notified.

1. 1Click 'Test & Review' to execute the code
2. 2Check the output for 'conflict_detected' field
3. 3Verify 'conflict_details' shows readable conflict information
4. 4Click 'Continue' if the test completes without errors

Filter > Condition Setup

Add Filter for Conflicts Only

Add a filter so Slack only gets messaged when conflicts actually exist. Without this, every calendar event would trigger a Slack message.

1. 1Click the '+' icon and select 'Filter by Zapier'
2. 2Set the condition to 'Only continue if...'
3. 3Choose 'Conflict Detected' from the Code step output
4. 4Set the condition to 'Exactly matches' and value 'true'

Action > Slack > Send Channel Message

Connect Slack to Zapier

Establish the connection to your Slack workspace so Zapier can post messages to your office channel. This requires Slack workspace admin permissions.

1. 1Click '+' to add another action step
2. 2Search for 'Slack' and select it
3. 3Choose 'Send Channel Message' as the action
4. 4Click 'Sign in to Slack' and authorize the Zapier app

Slack Setup > Message Configuration

Configure the Slack Alert Message

Set up the channel destination and message content for conflict notifications. The message should include event details and conflict information to help resolve the issue.

1. 1Select '#office' (or your preferred channel) from the Channel dropdown
2. 2Set Message Text to include conflict details from the Code step
3. 3Add event title, time, and conflicting event info using mapped fields
4. 4Enable 'Send as Bot' for consistent message formatting

📬 New entry: {{1.name}}
Email: {{1.email}}
Details: {{1.description}}

Slack Setup > Test & Review

Test the Complete Workflow

Run the entire Zap end-to-end to verify conflicts are properly detected and Slack messages are formatted correctly. This catches any mapping issues before going live.

1. 1Click 'Test & Review' in the Slack step
2. 2Check your Slack channel for the test message
3. 3Verify the message contains correct event details and timing
4. 4Click 'Turn on Zap' if the test succeeds