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Whatnot interview notes, page 1 of 4

Mid-sized

Most of these Whatnot write-ups come from Software Engineers (25), then Machine Learning Engineers (3) and Mobile Engineers (3). The most reported rounds are the technical phone screen (20), the system design round (7), the product sense round (3) and the hiring manager screen (1).

32 interview notes · updated Sep 2026

Whatnot·Software Engineer·Onsite - System Design / Architecture

Apr 2026
System design round at Whatnot for a software engineer role. The whole thing was basically one big question about building a competitive programming platform at scale, and they wanted real depth across execution, storage, and reliability rather than a surface-level sketch.
  • Design a large-scale online coding practice and contest platform that supports problem browsing, multi-language submissions, sandboxed execution, verdicts, submission history, and timed competitions with leaderboards.
  • How would you handle compiling, sandboxing, and executing user-submitted code safely and at scale?
  • How would you use signed URLs to handle uploading and downloading large test data, execution logs, or other artifacts?
  • How would you scale the platform to handle a high-traffic competition with tens of thousands of concurrent participants and submission spikes?
  • What are the key reliability, security, and observability concerns for a platform like this, and what trade-offs would you make?

“I started with the data models and APIs which felt safe, but I spent way too long there and then had to rush through the execution pipeline.”

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Whatnot·Software Engineer·Technical Phone Screen

Apr 2026
Coding round at Whatnot for a software engineer role. One of the questions was a sorted squares variant, pretty close to a well-known leetcode problem.
  • Given a sorted array of integers, return a new array of the squares of each element, also in sorted order.

“Classic two-pointer setup if you know it, but I went with sort-after-squaring first and they pushed me to optimize.”

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Whatnot·Machine Learning Engineer·Hiring Manager Screen

Apr 2026
Behavioral hiring manager screen for an ML engineer role at Whatnot, about 30 minutes, two main topics: your background and why this team, plus a product improvement question. Pretty standard format but the product question had some real teeth to it.
  • Walk me through your background and tell me what specifically draws you to this team and product.
  • What improvements or new features would you suggest for Whatnot? Walk me through a specific user pain point, your proposed solution, and how you'd measure whether it worked.

“I had a decent answer for the background part but fumbled the 'why this team' bit.”

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Whatnot·Software Engineer·Technical Phone Screen

Apr 2026
Coding screen for a software engineer role at Whatnot. Two problems, each with a follow-up that made the easy version feel like a warm-up. The string one was manageable but the array squares problem with negatives took me a minute to think through properly.
  • Given a string, repeatedly remove adjacent pairs of identical characters until none remain. What's your approach and complexity, then implement it.
  • Extend the previous problem: instead of pairs, remove any contiguous run of exactly k identical characters. Handle the cascading effect where removing one group can trigger another.
  • You have two sorted nonnegative integer arrays. Merge and return a sorted array of their squares. Aim for linear time.
  • Same problem but now both arrays can contain negative numbers. How does your approach change?

“Stack is the right move here and I knew it pretty fast.”

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Whatnot·Software Engineer·Technical Phone Screen

Apr 2026
Whatnot gave me a 45-minute implementation interview for a mobile engineer role where the whole thing was basically one big state-management puzzle dressed up as a feature build. Not the worst format I've done, but the time pressure made it spicy.
  • Build a small mobile app with two list screens that fetch data from a mock API. Items can appear in both lists, and updates to an item in one list must automatically reflect in the other. How do you approach the state management and how do you allocate your time across 45 minutes?

“The item-sync requirement is where it gets interesting.”

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Whatnot·Software Engineer·Onsite - Product Sense / Strategy

May 2026
Product sense question for a software engineer role at Whatnot. One question, open-ended, and they wanted the full package: problem, users, feature, metrics, experiment design, guardrails, the works.
  • You're working on a consumer mobile app. Propose one product improvement to boost engagement, retention, or conversion. Walk through the user problem, the affected segment, what you'd build, how you'd implement it, what metrics you'd track, how you'd run an experiment, what guardrails you'd watch, and any risks to other users.

“This is a lot to cover in one question and I underestimated how long the metrics and experiment sections would take.”

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Whatnot·Software Engineer·Technical Phone Screen

May 2026
Whatnot SWE interview with a dynamic programming problem on knight moves across a phone keypad. Clean problem statement, but the modular arithmetic constraint and the 5000-hop upper bound meant a naive recursive approach was a non-starter.
  • Given a chess knight placed on a phone keypad, write a function that counts the number of distinct digit sequences the knight can dial starting from a given digit after exactly N hops. The keypad has two unusable corner cells, and the answer should be returned modulo 10^9+7.

“My first instinct was recursion with memoization which felt fine until I noticed the hop count could go up to 5000.”

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Whatnot·Software Engineer·Technical Phone Screen

May 2026
Whatnot software engineer interview with four coding questions back to back, each requiring a walkthrough of the approach before writing any code. The pace was brutal and I was using Java which did not help. Ended with bugs in my output and no time to clean anything up.
  • Coding problem 1: implement a solution and walk through your approach before writing any code.
  • Coding problem 2: second in a series of four questions, same format of discuss then implement.
  • Coding problem 3: third question in the sequence.
  • Coding problem 4 with a follow-up: extend your solution to handle negative numbers in the input data.

“They wanted to hear the plan before any code went down.”

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Whatnot·Software Engineer·Technical Phone Screen

May 2026
Whatnot software engineer interview with a coding problem around message filtering. The question was more implementation-focused than algorithmic but had a few gotchas that made it less trivial than it looked.
  • Given an array of message dictionaries (each mapping a username to a message string) and a list of unsafe words, return only the messages where none of the unsafe words appear as whole words. Make sure punctuation is handled correctly so that something like 'damn,' still matches the unsafe word 'damn'.

“The whole-word matching piece is where I almost tripped up.”

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Whatnot·Software Engineer·Onsite - System Design / Architecture

May 2026
System design round at Whatnot for a software engineer role. The main question was the classic 'design LeetCode' problem, followed by two targeted follow-ups that got more interesting than the base question.
  • Design a platform like LeetCode, including its core features and architecture.
  • How do signed URLs work, and when would you use them in this system?
  • How would you scale the system to support live competitions with many concurrent users?

“Pretty well-trodden territory if you've done any system design prep.”

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