Slack MTS interview experience
Anonymous User
801
SlackInterview

Hi Community,

During my preparation, I couldn't find many detailed Slack interview experiences online—especially for backend roles. So, I wanted to share mine in the hope it helps others preparing for similar roles.

Background:

I applied for an MTS/SMTS Backend Engineer role at Salesforce a couple of months ago. After about 2 months, I was contacted by a Talent Coordinator—but things were a bit unusual from the start:

  1. The role I applied for no longer existed on the portal.

  2. No one from Talent Acquisition reached out to confirm my experience or explain the role—unlike how most companies usually operate.

The Talent Coordinator directly scheduled a Hiring Manager round to assess my fit.

Hiring Manager Round:

  • The interviewer was a Director of Engineering at Slack (US-based).

  • We started with introductions, followed by behavioral questions like:

    1. Tell me about a time when you couldn’t complete a task on time.

    2. Describe a conflict with a coworker and how you handled it.

I answered using the STAR (Situation, Task, Action, Result) format with real examples from my experience.

Technical Discussion:

He gave a scenario:

"Assume you’ve taken over a project and noticed network calls are showing 50% higher latency. The original owner has left. How would you debug it?"

I discussed the domains I’d investigate (network, backend, infra, DB, etc.). He seemed satisfied.

Next:

"How would you implement an @autocomplete feature in Slack?"

I described an approach similar to Google Search Autocomplete:

  • Rank-based Trie

  • Client + Server-side caching

  • Query optimization

He looked satisfied with the explanation.

Long Gap (3 Weeks):

I assumed I was rejected. But then another Talent Coordinator reached out for a Problem Solving round and asked for availability.

However, I received two different schedules from two different coordinators:

  • One showed a 1.5-hour round

  • The other showed a 1-hour round

Up to this point, I still believed I was being interviewed for a Salesforce role.

Upon checking the interviewer's LinkedIn, I realized the role was actually for Slack. Not my fault, there were no formal communication or role clarification from the Talent Acquisition team.

I tried to follow up via email and phone to get clarity on the role and round format, but received no response. This was quite strange and disappointing.

Eventually, the 1.5-hour round was confirmed, and I joined the round without knowing the exact format or expectations.

Problem Solving Round (Nano Slack):

The interviewer explained the format:

  • 20 minutes: Go through the Nano Slack codebase (a simplified Slack implementation). You can ask questions during this time.

  • 1 hour: Implement the missing functionalities based on the provided requirements.

  • 10 minutes: For scaling discussion and Q & A.

There were 4 requirements in total:

  • I fully implemented 2

  • For the 3rd, I provided a clear approach

  • All existing and new test cases were expected to pass

The interviewer was helpful and guided me when I got stuck.

Result:

Two days later, a 4th Talent Coordinator contacted me saying I cleared the round and was being moved to the Architecture + Behavioral round.

Architecture Round:

This was conducted by a Staff Engineer.

Scenario:

"Imagine Slack wants to support third-party integrations. For example, if two users want to integrate with Jira, OneDrive, BookMyShow, etc., how would you design this?"

The requirement was vague, and I spent ~15-20 minutes asking clarifying questions (not sure if I ever fully understood what he wanted).

To proceed, I focused on a Jira-like integration and proposed a Pub/Sub notification system:

  • When users subscribe to a Jira item, any updates would trigger Slack notifications to all subscribers.

I discussed:

  • Entities

  • Pub/Sub model

  • Database choices

  • Caching strategies

  • Message queues and why I chose a particular one

He asked me to skip Entity, API contracts and assume those were already taken care of.

We did some discussion at the end about the Failure recovery mechanisms and alternatives and i provided couple of options for each.

He took a screenshot of my design and wished me luck (which I later realized was for my job search, not for progressing in the process 😅).

Final Outcome:

Two days later, I received a notification that the Behavioral round was cancelled. Upon following up, I was told that the feedback from the Architecture round was not positive, hence the cancellation.

I requested feedback, and the coordinator said he would check with the Talent Acquisition team. Haven't received till now.

15 days later, I received a rejection email.

Final Thoughts:

If you're preparing for Slack's Backend roles, especially the Design round, please prepare well for vague and open-ended integration system design questions.

I genuinely hope this experience helps you avoid surprises and prepare better.

If you found this useful, please upvote. Also, feel free to share your own experience—especially around the System Design round.

Good luck, everyone!

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