Roblox Interview Questions — Page 6

Roblox·Data Scientist·Technical Phone Screen

May 2026

Roblox DS interview with a deep dive into ads marketplace experimentation. The whole thing was basically one long case study and they expected you to go several layers deep on each part. Pretty intense.

For an experiment testing increased ad load and a higher floor price in a mobile ads marketplace, how would you choose the unit of randomization, and how would you handle interference risks like auction dynamics or supply constraints?
What primary KPI and guardrail metrics would you use to make a go/no-go decision, and what are your exact success and stop-loss thresholds?
Walk through the power analysis for this experiment. What sample size, traffic split, and duration do you need for 90% power at alpha 0.05 to detect a 10% lift in daily revenue per user?
How would you control for bias in this experiment? Cover pre-experiment covariate adjustment, seasonality, and your approach to sequential versus fixed-horizon testing, including how you'd handle multiple variants.
How would you detect advertiser-side cannibalization and shifts in clearing prices when running this experiment? What diagnostics would you look at?

“This is where I stumbled first.”

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Roblox·Software Engineer·Technical Phone Screen

May 2026

Roblox SWE interview that went deep on rate limiting, both the implementation side and the system design side. Two-part coding problem with a follow-up discussion that felt more like a design round than a coding one.

Implement a sliding window rate limiter that takes a stream of (user_id, timestamp) requests and decides whether each request is allowed, given a window size W and a max of N requests per window per user.
Extend the rate limiter to handle per-user AND per-game limits simultaneously. Each request is (user_id, game_id, timestamp) and must pass both a user-level check and a game-level check. If either check fails, reject the request without consuming capacity from either limiter.
How would you extend this rate limiter to a distributed setting? What changes to the data structures and consistency guarantees would be needed?

“I went with a deque per user key, dropping timestamps outside the window before each check.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Roblox for a software engineer role, focused entirely on building a human-in-the-loop review pipeline for audio content moderation. Big question, lots of moving parts, and I definitely underestimated how deep they wanted to go on the operational side.

Design a human-in-the-loop review subsystem for audio content moderation. Walk through how detections become review tasks, how you triage them into queues by severity, what the reviewer UI needs, SLAs, sampling and consensus mechanisms for quality, gold-standard audits, escalation and requeue logic, access control for sensitive audio, audit logging, how reviewer feedback feeds back into model thresholds and training data, and how you'd plan reviewer capacity and control backlog.

“This was one question but it basically had twelve sub-questions baked in.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Roblox for a software engineer role, focused entirely on building a like/unlike feature at massive scale. The question had a lot of moving parts and pushed into some areas I hadn't fully thought through before.

Design a Like/Unlike feature for a social platform that handles millions of read requests per second, shows total like counts, shows whether the current user has liked an item, and optionally lists users who liked an item with pagination.

“I started with the data model, a user_likes table with a composite key, and that part went fine.”

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Roblox·Machine Learning Engineer·Technical Phone Screen

May 2026

Went through a project presentation round for an MLE role at Roblox and it was kind of a weird experience. I kept pausing between slides to invite questions and got nothing, just silence. The only thing the interviewer asked at the very end was a token question about my role, which felt more like a formality than actual curiosity.

What was your specific role and contribution in the project you presented?

“Asked at the very end, clearly as an afterthought.”

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Roblox·Data Scientist·Onsite - Behavioral / Leadership

May 2026

Behavioral loop for a Data Scientist role at Roblox. Heavy on structured storytelling and self-reflection, less about technical depth than I expected. The questions pushed pretty hard on motivation and team dynamics.

Walk me through a professional and a personal story that show you're the right fit for this role, including your context, the decisions you owned, any trade-offs or mistakes, and the measurable results.
What's driving you to look for something new right now? Break it down into what's pushing you away from your current situation versus what's pulling you toward this opportunity, and tell me what your non-negotiables are.
Take me through one past project from start to finish, the skills you applied, and what you'd change if you did it again.
Describe the team structure and working environment where you've been most effective. How did you handle situations where roles were unclear or conflict came up?
How do the experiences you've shared map to what you'd actually do in your first 90 days here?

“This is basically a two-story gauntlet.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

May 2026

System design round at Roblox for a software engineer role, focused entirely on building a like/dislike system from scratch. The interviewer pushed hard on trade-offs and wanted proactive driving, not just answering questions.

Design a like/dislike system where users can react to items, switch reactions, or remove them, and the system supports per-user reaction lookup, per-user liked item history, and per-item like/dislike counts.
How do you ensure react() is idempotent and handles exactly-once semantics when the same request arrives multiple times?
What database would you choose for storing user reactions and item counts, and how would you design the schema?
How would you shard the data, and what are the trade-offs between sharding by userId versus itemId?
What are the read/write consistency trade-offs for serving like counts, and when is it acceptable to show a stale count?

“This is the whole interview basically.”

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Roblox·Frontend Engineer·Take-home Assignment

May 2026

Took a take-home for a frontend role at Roblox. The prompt was to build an image feed and they gave you the API plus pretty detailed specs, so it wasn't one of those vague 'build whatever' situations. The real meat was in infinite scrolling, offline support, and how well you tested the thing.

Build an image feed with infinite scrolling, offline support, and solid test coverage. An API and detailed requirements were provided.

“The spec was detailed enough that you couldn't really complain about ambiguity, which is kind of a double-edged thing.”

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Roblox·Data Scientist·Technical Phone Screen

May 2026

Roblox Data Scientist interview threw a pretty gnarly streaming systems question at me. The kind of thing where you think you know what they're asking and then realize halfway through you've been solving the wrong problem.

Implement a Python function that computes per-campaign click-through rate over a rolling 24-hour window from two event streams, with click deduplication and support for late-arriving events.

“This one wrecked me a little.”

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Roblox·Machine Learning Engineer·Technical Phone Screen

May 2026

Did a system design round for an MLE role at Roblox, and the whole session basically revolved around one problem that seemed simple but had a lot of layers once you started pulling on it. Came away feeling okay about it but not great.

Design a hit counter that tracks the number of hits received in the past 5 minutes. The counter accepts timestamps in seconds, calls arrive in non-decreasing timestamp order, and multiple hits can share the same timestamp. Walk through a deque-based solution and extend it to support per-user rate limiting using a dictionary of deques.

“I started with a naive array approach and they let me dig myself into a corner before asking about memory.”

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