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Roblox·Machine Learning Engineer·Onsite - System Design / Architecture·Senior

Senior
Apr 2026

Summary

Interviewed for an ML engineer role at Roblox and got a system design question about detecting bot players. Pretty open-ended, which I wasn't fully prepared for.

Questions Asked (1)

Q1

How would you design a system to detect bot players in a gaming platform?

System DesignTechnical Trade-offsProduct Analytics & Metrics
Author's notes

I went straight to feature engineering, things like click patterns, movement speed, session length, and tried to sketch out a pipeline from data collection to model serving.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the scope—what constitutes a bot, what data is available, and what the business impact is. Then propose a layered detection system combining rule-based heuristics, supervised ML models, and unsupervised anomaly detection, with a feedback loop for continuous improvement. Emphasize trade-offs between precision and recall, latency, and scalability, and how you'd measure success.

Pro tip: Frame the problem as an adversarial arms race: bots evolve, so your system must adapt. Mention the importance of human-in-the-loop review and how you'd handle false positives to avoid punishing legitimate players.

1. Clarify Requirements and Define Bot Behavior

Ask questions to understand what types of bots (e.g., aimbots, farming bots, spam bots) and what data is available (game logs, player reports, etc.). Define success metrics like precision, recall, and business impact.

2. Data Collection and Feature Engineering

Identify relevant data sources: player actions, session patterns, device fingerprints, network traffic. Engineer features that capture bot-like behavior, such as action frequency, timing regularity, and social interactions.

3. Model Selection and Training

Choose a combination of approaches: rule-based filters for known bots, supervised models (e.g., gradient boosting) using labeled data, and unsupervised anomaly detection (e.g., isolation forests) for novel bots. Consider deep learning for sequence data.

4. Deployment and Real-time Detection

Design a scalable pipeline for real-time scoring, with low-latency inference. Integrate with game servers to take actions (e.g., flag, ban, shadowban) and ensure the system can handle high throughput.

5. Evaluation, Monitoring, and Iteration

Set up A/B tests and offline evaluation. Monitor model drift and adversarial adaptation. Incorporate human review and player reports to create a feedback loop for retraining and improving the system.

Key Points to Mention

  • Trade-offs between precision and recall: high precision reduces false bans but may miss bots; high recall catches more bots but risks false positives.
  • Adversarial nature: bots adapt, so the system needs continuous learning and possibly adversarial training.
  • Scalability: handling millions of players in real-time requires efficient feature computation and model inference.
  • Explainability: for bans, you need to explain why a player was flagged, which may favor simpler models or post-hoc explanations.
  • Human-in-the-loop: combining automated detection with human review for edge cases and appeals.
  • Metrics: define success not just by model accuracy but by business metrics like reduction in bot activity, player retention, and support tickets.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.