Slack Software Engineer Interview Questions

1.Think back to a team meeting or design discussion where someone was clearly checked out or not speaking up. What did you do about it, and did it change anything?

2.Tell me about a code review comment you left — or received — that caused real friction. How did it get resolved, and what would you write differently today?

3.Describe a time when something a customer or user reported caused you to stop and reprioritize work you were already deep into. What was the signal, and what did you actually change?

4.Walk me through the hardest technical disagreement you've had with a peer or partner team in the last year or two. What was the core of the disagreement, and how did it actually get resolved?

5.Tell me about a time you actively worked to get a quieter or more junior teammate's idea seriously considered by the broader group — especially when it might have been easier to just move forward without them.

6.Tell me about a time you reviewed a PR where you had serious technical concerns but the author was either more senior than you or clearly emotionally invested in the code. How did you handle it, and what happened?

7.Slack's real-time messaging server needs to fan out a message to thousands of connected clients near-instantly. What are the core architectural pieces you'd lean on to make that work reliably?

8.You're adding a feature flag to a new Slack Workflow Builder capability that's rolling out to 1% of workspaces. Walk me through how you'd structure that in code and what could go wrong if you do it carelessly.

9.Slack's MySQL databases are sharded by workspace ID. A PM wants to build a cross-workspace analytics feature that surfaces the most active channels across your entire customer base. How do you approach this, and what would you push back on?

10.You're building a TypeScript React component for a Slack message composer that renders as the user types, but it's janky on long messages. Profiling shows a lot of time in re-renders. What's your debugging and fixing approach?

11.You're on-call and you see your SLO burn rate alert fire — the error rate on Slack's channel message delivery API has jumped from 0.1% to 4% in the last 10 minutes. Walk me through exactly what you do.

12.Slack Connect lets two companies collaborate in a shared channel. Design the permission and access control model for messages in a Slack Connect channel — specifically, what happens to those messages when one of the two organizations removes the other from the channel.

13.Design a read receipt system for Slack DMs — showing when someone has seen your message. How would you store and surface that data at scale?

14.Slack Workflow Builder lets non-technical users build automations that can trigger on channel events. How would you design the execution layer that actually runs those workflows reliably?

15.Design Slack's channel search — when a user types in the search bar and we need to return relevant messages from their workspace. How do you make it fast and accurate?

16.Design Slack Huddles' signaling layer — the part that lets two or more users discover each other and negotiate a peer-to-peer audio connection. Don't worry about the media server; just the signaling.

17.Design the backend for Agentforce in Slack — specifically the part where an AI agent answers a question in a channel by retrieving context from Salesforce CRM data. How do you make it fast, accurate, and safe?

18.Slack needs to deliver push notifications to mobile devices when a user is mentioned. Design the end-to-end pipeline from message send to push delivery, including how you'd handle a workspace with 10,000 members all @here-ing at once.

19.Tell me about a time you caught a bug or usability issue in your own work before it shipped. What made you stop and fix it instead of just moving forward?

20.Describe a time you were working on something alongside a designer and you disagreed with a design decision. How did you handle it?

21.Tell me about a time you had to onboard yourself into a confusing or poorly documented codebase. What did you do to get up to speed, and what did you leave behind for the next person?

22.Imagine a PM on your team pushes back on a feature estimate you gave — they say the timeline is too long and asks you to cut it down for the sprint. What do you do?

23.Tell me about a time your team shipped something that technically worked but that you later felt embarrassed by — not because it had a bug, but because of the experience it created for users. What happened and what did you do?

24.Tell me about a time you were new to a team and noticed a process or norm that you thought was slowing the team down. Did you do anything about it, and if so, how?

25.Estimate how many messages Slack processes per second on a typical weekday. Walk me through how you get there.

26.Slack Connect lets companies share channels with external partners. If you were trying to estimate the customer-support cost saved when a company moves their vendor relationship from email to a Slack Connect channel, how would you approach it?

27.Slack's weekly active workspace metric dropped 3% month-over-month across the mid-market segment. No major incidents, no big product changes. How do you diagnose what happened?

28.Slack is deciding whether to invest engineering resources in improving Workflow Builder's reliability or in shipping three new workflow trigger types. How would you frame the tradeoff to help the team make a good decision?

29.Estimate the total storage cost Slack incurs per year just from file attachments — images, PDFs, the things people drag into channels. Walk me through your reasoning.

30.Slack is considering charging enterprise customers for Slack AI features like channel summaries and search. How would you think about what to measure to know if that's working — not just revenue, but whether it's actually working?