Slack System Design Interview Questions (2026): 10 Prompts + How to Answer
Slack system design practice is one slice of a 50-prompt set. Narrate the user and the API before you draw boxes. Call out the bottleneck you are willing to leave for a later version. Mention retention and legal hold if the customer is a large company. Chat is not only a green dot.
System design practice for Slack: sketch channel message delivery for read-heavy traffic. Start with the API and the data you store, then add one cache and say what it does not cover.
How to approach. Users and API first. For channel message delivery, say the one request you must make fast and the one you can delay.
Design workspace search the way a Slack round expects: a single-region failure should not take the product down. Say what you would refuse to build in the first conversation.
How to approach. Draw one failure domain and what still works. Slack interviewers listen for what you explicitly will not build yet.
Design prompt for Slack: a workflow builder run needs an API that a client can retry safely. Define the idempotency key and what the user sees on a timeout.
How to approach. Retries need an idempotency story. Say what the client sends the second time and what the user sees.
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