Roblox Interview Questions — Page 13

Roblox·Software Engineer·Technical Phone Screen

Jun 2026

Roblox SWE interview that was basically one big coding problem split into two parts, both centered on rate limiting. The second part is where things get interesting and where I think most people either shine or completely fall apart.

Design and implement an in-memory sliding-window rate limiter that tracks requests per user. The API should be a single method that takes a user ID and a timestamp in milliseconds, and returns whether the request is allowed given a max of N requests in the last W milliseconds.
Extend the rate limiter so each request also carries a game ID. A request is only allowed if it passes both a per-user limit and a per-game limit independently. How do you structure this, and what are the complexity and eviction trade-offs?

“My first instinct was a fixed window and I had to catch myself before saying it out loud.”

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Roblox·Software Engineer·Technical Phone Screen

Jun 2026

Roblox software engineer round focused on a single meaty coding problem around program trace reconstruction. Pretty systems-flavored for what felt like a standard technical screen, and the follow-up pushed into parsing flexibility which I wasn't fully ready for.

Given a stream of function-entry and function-exit events from a running program, reconstruct the call stack. You need to parse the trace input, maintain the active stack, and be able to report the current stack state at any point.

“My first instinct was just a plain stack with push on entry and pop on exit, which is correct but I spent too long explaining it before writing any code.”

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Roblox·Data Scientist·Technical Phone Screen

Jul 2026

Roblox data scientist technical screen, basically one big coding problem about implementing p-values from scratch in Python. Pretty brutal if you haven't touched stats internals in a while.

Implement a Python function that computes the p-value for one-sided and two-sided hypothesis tests, supporting both z and t distributions, without relying on external libraries for the z-distribution CDF.
How do you handle edge cases like NaN or infinite inputs, degrees of freedom less than 1, and extreme test statistic values in a statistical computation function?
Walk through how you would verify the correctness of your implementation using unit tests, including specific known values and monotonicity checks.

“This was the whole interview.”

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Roblox·Machine Learning Engineer·Technical Phone Screen

Jul 2026

Got a coding question from Roblox for an ML Engineer role that was basically a topological sort with a specific deterministic leveling rule. The problem was well-defined but the edge cases around missing deps and cycles needed careful handling.

Given a list of component dependency declarations, return a valid build order where each component appears only after all its dependencies. The order must follow a deterministic wave-based leveling rule: at each step, all components whose dependencies are satisfied get emitted together, sorted by their original declaration index. Return an error if any dependency is undeclared or if there's a cycle.

“The core of it is Kahn's algorithm but the twist is you can't just do a standard BFS and call it done.”

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Roblox·Software Engineer·Technical Phone Screen

Jul 2026

Roblox technical phone screen for a software engineering role, one algorithmic question about robot movement simulation. Pretty focused session, no fluff, just code and complexity analysis.

A robot starts at the origin facing north on an infinite 2D grid. It follows a command string of move-forward, turn-left, and turn-right instructions. Given that this string is repeated up to a billion times, implement a solution that (a) returns the robot's position and direction after one pass of the string, and (b) determines whether the robot's path stays bounded if the string repeats forever. What are your time and space complexities, and how do you avoid simulating all repetitions?

“The key insight I kept circling around was that you only need to simulate one cycle.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Roblox for a software engineering role. The whole thing was basically one big question about matchmaking infrastructure, and they went deep on every layer of it.

Design a matchmaking system where users join a waiting queue and get matched into a game. Walk through the architecture, data model, and the matching algorithm itself.
How do you ensure fairness in matchmaking while keeping wait times low, and what happens when those two goals conflict?
How does your system handle timeouts, user cancellations, and clients that retry a matchmaking request?
How would you extend the system to support constraints like team size, geographic region, and player skill level all at once?
The system needs to handle massive concurrency. How do you shard the queue and avoid hot spots?
Walk through the reliability concerns: idempotency, failure recovery, backpressure, and how you'd observe the system in production.

“I started with a basic queue and a polling worker, which felt a bit naive in retrospect.”

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Roblox·Software Engineer·Technical Phone Screen

Jul 2026

Roblox SWE interview with a system design coding question focused on rate limiting and bot detection. Pretty meaty for a single problem, they wanted you to think through the whole thing from data structures to memory management.

Design and implement an IP-based bot detection system. It should track how many requests each IP makes within a sliding time window, flag IPs that exceed a threshold, and periodically clean up stale data to keep memory bounded. Implement record(ip, timestamp) and isBot(ip, timestamp).

“I went straight for a per-IP deque of timestamps, which felt right.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Roblox for a software engineer role, focused entirely on designing a Likes system from scratch. The depth they expected was pretty serious, covering everything from schema choices to handling celebrity items under load.

Design a Likes system that supports liking/unliking items, checking if a user has liked something, listing a user's liked items with pagination, and fetching total like counts per item. Focus on scalability and data schema.

“This one sprawled fast.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Roblox for a software engineer role, focused entirely on building a like/unlike system that could handle massive write throughput. Pretty deep dive, they pushed hard on the tradeoffs.

Design a Like/Unlike system that can operate at scale, supporting operations like liking a post, unliking it, fetching like counts, checking if a user has liked something, and showing a user's liked posts feed.

“This one went longer than I expected.”

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Roblox·Software Engineer·Onsite - System Design / Architecture

Jul 2026

System design round at Roblox for a software engineer role, focused entirely on designing a matchmaking system for a multiplayer game. Covered a lot of ground in one question, which was both interesting and a bit overwhelming.

Design a matchmaking system for an online multiplayer game. Walk through requirements like game modes and party size, your high-level architecture, how you'd handle skill-based bucketing and region sharding, how you'd balance match quality against wait time, what happens when players go stale or drop out of queue, fairness and anti-smurf measures, and how the system scales to millions of concurrent players.

“This is a beast of a question.”

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