Microsoft is just minutes away from unveiling its Slack competitor, Microsoft Teams, at an event in New York City today. The software giant is expected to position its Teams software with tight integration into Microsoft Office, Skype, and the company's Office 365 services, and as a direct competitor to Slack. Microsoft hasn't even officially unveiled its Teams service, but that's not stopping Slack from getting some words out before the software maker's event.

In a full back page ad in the New York Times, Slack welcomes Microsoft's competition into the messaging market with some "friendly advice." In a long note, that's also published on Slack's blog, the company warns Microsoft that it's not the features that matter, it's the craftsmanship and human aspects of the software. "We've spent tens of thousands of hours talking to customers and adapting Slack to find the grooves that match all those human quirks," says the Slack team. "The internal transparency and sense of shared purpose that Slack-using teams discover is not an accident. Tiny details make big differences."

That feeling when you think "we should buy a full page in the Times and publish an open letter," and then you do. pic.twitter.com/BQiEawRA6d — Stewart Butterfield (@stewart) November 2, 2016

Despite being a closed-source software-as-a-service tool, Slack claims that "an open platform is essential" in its warning letter to Microsoft. "The modern knowledge worker relies on dozens of different products for their daily work, and that number is constantly expanding," explains the Slack team. "These critical business processes and workflows demand the best tools, regardless of vendor."

Slack has done a wonderful job at integrating many services into its product, but this doesn't make it an open platform that people can contribute to freely. There are 750 apps in the Slack App Directory, but any of those could disappear at any point because Slack controls the keys. Nobody is expecting Microsoft to do anything different, as that's the key selling point of providing this software as a service to millions of customers, so it's odd to see Slack position itself as "open" in the sense of software.

Slack advises Microsoft to focus on love

The final point in Slack's note is an important one, it's all about love. "You'll need to take a radically different approach to supporting and partnering with customers to help them adjust to new and better ways of working," warns the Slack team. "If you want customers to switch to your product, you're going to have to match our commitment to their success and take the same amount of delight in their happiness." That's something Microsoft, as a corporate giant, will have to adjust to, and Slack will always have the edge and focus there.

Slack ends its ad with a defiant message that it's here to stay, no matter what Microsoft announces today, and welcomes the software maker "to the revolution." The entire note sounds like Slack is worried about Microsoft's entry into this market, and the company even admits "it's a little scary." As Ben Thompson points out on Twitter, it's also eerily similar to Apple's welcome to IBM and its personal computers in the Wall Street Journal in 1981, or Rdio's response to Apple Music. We all know how both of those worked out.

Slack has many reasons to fear Microsoft

Slack has many reasons to fear Microsoft today. While the chat service has seen impressive growth with 4 million daily active users, it's yet to break into all of the big companies that are dominated by Microsoft's productivity tools. Slack has managed to hit 28 out of Fortune 100 companies, and some key customers include IBM, eBay, EA, Pinterest, TIME, and LinkedIn. It all depends on how Microsoft positions Microsoft Teams, but if it's part of what a business is already paying for with Microsoft Office, then it might make many technology officers think twice about paying for Slack on top. We'll find out a lot more about Microsoft Teams at 11AM ET today, and The Verge will be covering Microsoft's news as it happens.