If you self-host Tymeslot, complete these steps first; the connection fails without them. On tymeslot.app they are already done, so go straight to step 1.
A Microsoft Azure app is registered with
OUTLOOK_CLIENT_ID
and
OUTLOOK_CLIENT_SECRET
set in your environment (see the
Microsoft Azure App Setup
guide if you haven't done this yet)
The
Calendars.ReadWrite
delegated permission is added to your Azure app registration under
API permissions
Tymeslot is reachable over HTTPS, because Microsoft's OAuth callback requires a secure URL
Outcome
By the end of this guide, Tymeslot will check your Outlook Calendar for conflicts before offering a time, and create a calendar event for every confirmed booking.
How Outlook Calendar sync works
Tymeslot connects through the Microsoft Graph API using the
Calendars.ReadWrite
permission. It works the same way for personal Outlook.com accounts and Microsoft 365 work accounts.
Checking availability
When someone opens your booking page, Tymeslot reads the events in your selected calendars to work out which times are taken. Event details are used to show your events on your own Tymeslot dashboard calendar; your invitees only ever see open and taken times.
Creating booking events
When a booking is confirmed, Tymeslot writes an event into the meeting type's booking calendar, with the invitee's name and the meeting link. Rescheduling or cancelling in Tymeslot updates or removes that event. Tymeslot does not change events it did not create.
Real-time sync (optional)
By default, Tymeslot polls Outlook for calendar changes every 15 minutes. Your booking page
reads your calendars live, so bookings stay accurate; only your dashboard calendar can
lag behind. To have Microsoft push changes the moment they happen (through Graph
subscriptions), set the
WEBHOOK_BASE_URL
environment variable (see the
Environment Variables
reference). Existing connections switch to push when you reconnect them.
1
Connect Outlook Calendar
1
Navigate to [Dashboard]
→ [Integrations]
→ [Calendars].
2
Click [Connect a calendar]
and pick the [Outlook Calendar]
card. You are redirected to Microsoft's permission screen.
3
Sign in with your Microsoft account (personal Outlook.com or a Microsoft 365 work account). Microsoft shows the permissions Tymeslot is requesting.
4
Click [Accept]. Microsoft sends you back to the Integrations page. Your default calendar is already selected for conflict checks and set as the calendar bookings go to.
Outlook Calendar sits next to Google Calendar in the provider picker.
2
Select your calendars
Tymeslot finds every calendar in your Outlook account. Two separate settings decide how they are used:
Calendars checked for conflicts
Click [Manage calendars]
on the Outlook connection and tick every calendar that should block your availability. When an event in a ticked calendar is not set to Show As: Free, that time disappears from your booking page.
Where bookings are written
Each meeting type writes its bookings to one calendar, its Booking Destination. Open the meeting type, choose the Outlook account under 1. Select Calendar Account, then the calendar under 2. Select Specific Calendar. Until you choose, bookings go to your default calendar.
🔍
How conflict detection works
Outlook's Show As
field determines whether an event blocks your Tymeslot availability.
Show As value
Blocks availability?
Busy
Yes, the slot is unavailable
Free
No, the slot stays open
Tentative
Yes, the slot is unavailable
Out of Office
Yes, the slot is unavailable
Working Elsewhere
Yes, the slot is unavailable
Calendar connects but blocks no time?
Check that your Outlook events are not set to Show As: Free. Free events are ignored on purpose, so that placeholders and reminders don't block your bookings. Declined meetings and cancelled events don't block time either.
🏢
Microsoft 365 and work accounts
Both personal Outlook.com and Microsoft 365 work accounts are supported. Work accounts can need one extra step: admin consent.
Admin consent:
A Microsoft 365 organisation can require an IT administrator to approve third-party apps before users connect them. With that policy in place, the connection stops at a "Need admin approval" screen.
Exchange on-premises:
Not covered by this integration. The Graph API does not reach on-premises deployments, so use the
Microsoft Exchange integration
instead, which speaks EWS directly to a server your organisation runs.
Shared and delegated calendars:
Only your own calendars are supported. Calendars other people share with you, or delegate to you, need extra Microsoft Graph permissions that Tymeslot does not request.
'Need admin approval' during connection
Your Microsoft 365 organisation requires admin consent for third-party calendar access. Ask your IT admin to open the Azure portal → your app registration →
API permissions
→ Grant admin consent for [organisation]. Once granted, everyone in the organisation can connect without asking again. If you cannot wait, use a personal Outlook.com account in the meantime.
🔧
Troubleshooting
"Access denied" or "AADSTS" error during connection
Make sure the
Calendars.ReadWrite
delegated permission is added to your Azure app under API permissions, and that admin consent has been granted for organisational accounts.
"Invalid redirect URI"
The redirect URI in your Azure app registration must exactly match the one Tymeslot uses, including the
https://
prefix and the full path. Check the URI in your Azure app's
Authentication
settings.
Calendar connects but bookings still go through when busy
Check two things: (1) the right calendar is ticked under
[Manage calendars]
on the Outlook connection, and (2) the Outlook events in question are not set to Show As: Free.
Bookings are confirmed without a Teams link
Calendar sync and
Microsoft Teams
ask different things of the account: syncing needs a calendar, hosting a meeting needs a Teams
licence. Where the connected account has no licence that can host one, bookings still go
through, with no join link in the confirmation email.
❓
Frequently Asked Questions
Outlook Calendar sync works for my personal account but not my work Microsoft 365 account. Why?
A Microsoft 365 organisation can require admin consent before users connect third-party apps. With that policy, sign-in stops at a "Need admin approval" screen. Your IT administrator needs to open
portal.azure.com
→ your app registration → API permissions
and click Grant admin consent for [organisation]. Once granted for the tenant, everyone in the organisation can connect without asking again.
My calendar events appear in Outlook but my availability is not being checked. What's wrong?
Check that the right calendar is ticked under [Manage calendars]
on the Outlook connection. An Outlook account can hold several calendars, and Tymeslot only checks the ones you tick. Also confirm the events in question are not set to Show As: Free: Free events are ignored on purpose, so that placeholders and reminders do not block your availability.
Can I sync with a shared or delegated Outlook calendar?
No. Tymeslot supports only your own calendars. Calendars shared with you or delegated to you need extra Microsoft Graph permissions (such as Calendars.Read.Shared) that Tymeslot does not request.
Events I create manually in Outlook are not blocking my availability in Tymeslot. Why?
Check two things. First, the calendar holding those events must be ticked under
[Manage calendars]
on the Outlook connection; with several calendars, only the ticked ones count. Second, the events must not have
Show As
set to Free, because Tymeslot ignores Free events so that reminders and placeholders do not block bookings. If you only just created the events, give it two minutes: the booking page keeps what it reads from your calendar for that long.
Does Outlook Calendar sync work with on-premises Exchange?
Not this integration. Tymeslot connects here via the Microsoft Graph API, which only covers Exchange Online (Microsoft 365) and personal Outlook.com accounts; an on-premises Exchange Server does not expose the Graph endpoints it depends on.
On-premises Exchange has its own integration, which speaks Exchange Web Services with a username and password. See
Microsoft Exchange Integration
. It both blocks your availability and receives your bookings.
✅
Verify the integration is working
1
Open Outlook and create a test event covering a time slot that would otherwise be bookable. Confirm its
Show As
is set to Busy.
2
Open your Tymeslot booking page in a separate browser window. Navigate to the date of the test event.
3
Confirm the time slot appears as unavailable. If it is still offered, check that the right calendar is ticked under [Manage calendars].
4
Book a different, open slot as a test. Confirm a new event appears in your Outlook calendar with the invitee's name and the meeting link.
Connect Tymeslot to Google Calendar. Busy, Tentative and Out of Office events all block bookings, so you are never double-booked, and every booking is added to your calendar.
Sync Tymeslot with CalDAV calendars: Nextcloud, Radicale, Baikal, Zimbra, mailbox.org, iCloud and Fastmail. Conflict checks and new bookings work without a Google or Microsoft account.
Connect Tymeslot to an on-premises Microsoft Exchange Server over EWS. Covers the endpoint URL, domain logins versus mailbox addresses, self-signed certificates, and the read-only limits.
