How Slack Integrates with Teams for Calling

After speculating how Slack might integrate with Teams and concluding that Slack would get no assistance from Microsoft to bridge the gap between the platforms, on April 1 (no joke!), Slack shared a page that reveals some information about how their integration works. You can download and install the Teams add-in from the page.

Leveraging Slack’s Existing Outlook Integration

It looks very much like Slack plan to read calendar information about Teams calls (easy to do with the Outlook Graph API), probably leveraging their existing integration with Outlook. When I wrote about that integration, I noted that “Slack supports the ability to join a Skype meeting if scheduled in Outlook. They don’t say anything about being able to join a Teams meeting but given that the relevant button invokes a URL to the meeting, I’d be surprised if the link generated by Outlook didn’t work.” This is exactly what seems to be happening. Figure 1 shows how Slack displays details of an Outlook meeting with a button to join a Teams meeting.

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Slack displays an Outlook meeting (image credit: Slack

How Outlook Connects to Teams

When you schedule a Teams meeting, the Outlook calendar item is updated with several properties that allow the user to join the meeting. One of the properties is a “deep link” for the meeting, essentially, a URI that Teams interprets to connect a user to a meeting set up on its platform. The URI looks something like this:

The button displayed by Slack doubtless invokes the URI for the meeting. Clicking it joins the user to the meeting in the same manner as if they joined it from Outlook.

Calling Provider

Another thing Slack has done is to allow users to choose Teams as their default calling provider (Figure 2). The code to make this happen is under Slack’s control and they don’t need any help from Microsoft.

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Figure 2: Teams as an option for Slack calling provider (image credit: Slack)

No Real Mystery

I wish I had waited till today to write my original piece on this topic as I would look a lot smarter. In any case, there’s no mystery in what Slack has done. They have leveraged the Outlook add-in model and use Teams deep links to connect to Teams meetings. That’s smart. Much smarter than me.


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Tony Redmond has written thousands of articles about Microsoft technology since 1996. He covers Office 365 and associated technologies for and is also the lead author for the Office 365 for IT Pros eBook.