tl;dr: Definitely would not recommend any of my engineering friends to apply here. I definitely would not apply here again. It's been a while since I've experienced an engineering interview process as broken and dysfunctional as Slack's.

More details:

After some aggressive recruiting (I received 3 cold emails from the recruiter within a span of 2 weeks), I agreed to an initial phone call. The recruiter was enthusiastic and, at the end of the call, said, "Let me know your availability for a phone screen ASAP, because the engineering manager would love to talk to you sometime in the next two days."

I emailed him my availability that evening, but I didn't hear from anyone for an entire week (a bad sign). After 1 week and 3 days, I finally had a phone screen scheduled, but the engineering manager did not impress me at all. He seemed very uninspired by his job and could not give a clear answer when I asked what Slack's engineering priorities were (another really bad sign when the engineering manager cannot provide a concise, clear answer on this).

The next day, the recruiter emailed me a coding challenge and stated that "all candidates must complete the coding challenge" as part of the interview process. The recruiter also told me that "the engineering manager personally reviews the code" and "Slack has a standard criteria for grading all challenge submissions."

I was hesitant at first but decided I didn't want to end my interview without giving the coding challenge a shot. I spent several hours over 2 days to complete and submit it. Again, I waited and didn't hear from anyone for another TWO ENTIRE weeks.

Finally, I got an email from the recruiter that was (literally) 1 sentence – just a generic, rejection template email. I replied and asked for some feedback on my coding challenge submission, or at least some feedback that was specific to my interview. The recruiter just replied, "We thought you were great. Unfortunately, I don't have any specific feedback because I have no idea how the coding challenges are graded. You can always try interviewing again in 6 months."

The entire process was frustrating and disrespectful. Treating candidates like this is just BS. At the end of the day, raising a ton of VC funding and being an unicorn startup does not grant Slack the right to treat candidates like this. Slack really needs to fix its company culture.

Initial recruiting phone call.

Followed by a technical phone screen with the engineering manager.

Followed by a coding challenge.