OpenSlot · Guides

Outlook free/busy explained: what others can see, and why some calendars show as unavailable

Free/busy is the part of your Outlook calendar that says when you are busy without saying what you are doing. It is what the Scheduling Assistant shows as coloured blocks, and it is the only thing tools like OpenSlot read.

What it contains

For each interval (usually 30 minutes) a single status: free, tentative, busy, out of office, or working elsewhere. No titles, no attendees, no locations, no bodies — unless your organization has chosen to share more detail, which is separate from free/busy.

Who can see yours

By default, everyone in your Microsoft 365 organization can see your free/busy; people outside it cannot, unless your admins have set up organization relationships or you share your calendar with them individually. That is why a scheduling tool inside your company can merge colleagues' calendars instantly, but can't see a client's.

"No free/busy information could be retrieved"

The usual causes: the person is outside your organization; they have restricted free/busy sharing in Outlook (Calendar → Share → Permissions → "Can view when I'm busy" is the normal setting); their mailbox is on a different system; or the address is a distribution list, not a mailbox. Ask them to set permissions to at least "when I'm busy", or schedule by sending your own availability instead.

Turning free/busy into a list

Reading free/busy in a grid is fine for one person; for a group across two weeks it is not. OpenSlot queries the same free/busy data for up to 40 people, merges it, and hands back the gaps as text:

All times in US/Eastern
• Today 07/08
  03:30 PM - 04:00 PM
  05:00 PM - 05:30 PM
• Thursday 07/09
  09:30 AM - 10:30 AM
  12:00 PM - 01:00 PM
  02:30 PM - 03:00 PM