I think that's exactly why OP's idea will take off. Everyone is too scared to build a competitor.

Airbnb started by spamming Craigslist with fake ads. Stripe started by accepting payments to a single bank account. Doing something shoddy/somewhat shady and not being afraid of the repercussions gets you ahead in startups.

So what if OP breaks someone's "TOS", by the time they notice or OP's product gets big enough too care, he will likely have sufficient enough capital to fight them off. If he never gets that big, more power to him for something that makes him some beer money.

I don’t think there would be any cause for Slack to complain for at least paid accounts. I glanced through the relevant terms, and there’s really only one even vaguely relevant topic, largely around competing with Slack.

In their App Developer Policy <https://api.slack.com/developer-policy>:

> As part of good business practices, Applications and developers are prohibited from: Circumventing Slack’s intended limitations (including pricing, features and access structures). You may not use the Slack API to replicate or compete with core products or services offered by Slack

And in their API Terms of Service <https://slack.com/intl/en-au/terms-of-service/api>, which cites the app developer policy and then adds:

> Further, you will not: … (C) access our APIs or documentation in order to replicate or compete with the Services

If Slack spell out that there being no public mirror is an intended limitation, or if they offer a direct equivalent, then they could complain. And they could do for free accounts, which have a history limit that this would incidentally circumvent. But for paid accounts I don’t believe either of these are true, so if it were limited to working with paid accounts I’d say you’d be in the clear with Slack for now. Of course, you’re still subject to their caprice in changing their rules, implementing new features, or just booting you off their platform even without cause at their whim, and that’s a significant existential risk for building such a business.

But I don’t think Slack would be particularly likely to boot them off, given that any hostile action on their part would be akin to claiming some degree of ownership of the data. The data belongs to the customer, and they should be able to do whatever they want with it without hindrance. Of course, such reasoning as this is only reasoning. If they did cut off such API access, they’d hardly be the first large company to shut the portcullis to support their own interests against their customers’; Twitter, for example.

It's an interesting question... In my experience at a number of companies / assignments, Slack made its way into the business through "the back door", so to speak; development teams started using it without prior business approval - in a lot of companies, the use of unmonitored chat services was a no-no, so a lot of people were stuck on e-mail or a Microsoft project. But through "grassroots" movements, Slack was shimmied into these companies and took off, until the management was convinced to start paying for it.

TL;DR I strongly believe Slack became popular through their users bending/breaking some rules.

I also believe that the users have the rights to archive and republish their chat messages as they please. I don't believe a service that archives messages will cause too much overhead to Slack either. They may start charging for API access though, which is fair.

I had the same thought. If I remember correctly, one of Slack's paid features is that you can retain older chat archives. This kind of circumvents that. Now, I think it's a cool product and I hope that there will be no legal repercussions.

He just needs to rebase to a country that doesn't really listen to US laws.