Reddit QA & SDET Interview Questions
Reddit hires quality and test engineers who can reason about a massive social platform: feeds and ranking, community moderation, ads, and experimentation, served at scale across web and mobile. The loop blends coding, test architecture, and a behavioral round.
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The interview process.
Reddit's quality-engineering loop generally runs a recruiter screen, a technical phone screen with coding, then a virtual on-site of 4 to 5 interviews: a coding interview, a test-architecture/system-design-for-testability interview, a mobile or backend interview depending on the team, and a behavioral round. Feed/ranking quality, scale, moderation, and experimentation recur across the loop.
Recruiter Screen
A 30-minute call on your background, interest in Reddit, and the team (feed, ads, safety, platform).
Technical Phone Screen
A 60-minute coding session with test-design follow-ups. Practical problem solving plus how you would test it.
On-Site: Coding
A hands-on coding interview focused on correct, well-tested code and solid fundamentals.
On-Site: Test Architecture & Testability
Design the test approach for a Reddit-style feature (the feed, voting, comments, search). Covers ranking quality, large-scale serving, and data correctness.
On-Site: Mobile or Backend
A platform-specific interview: mobile (feed performance, infinite scroll, offline) or backend (ranking services, vote counting, moderation tooling).
On-Site: Behavioral
A behavioral round on ownership, collaboration, and impact, with concrete examples expected.
What Reddit focuses on.
Key areas Reddit interviewers evaluate in QA and SDET candidates.
Feed and ranking quality: evaluating relevance and ranking where outputs are not exactly deterministic
Large-scale serving: testing systems that serve billions of feed and comment requests reliably
Moderation and safety: testing the tooling and protections that keep communities healthy
Experimentation quality: guarding A/B tests so experiments do not corrupt engagement metrics
Ads correctness: targeting, delivery, and measurement where money is involved
Mobile and web performance for a content-heavy, infinite-scroll product
Sample interview questions.
Questions based on real RedditQA interview patterns. Practice answering these with AssertHired’s AI interviewer.
- 01
How would you test a feed-ranking feature where there is no single correct output?
- 02
How would you test vote counting so it is accurate and resistant to manipulation at scale?
- 03
How would you guard an A/B test on the feed so the experiment does not corrupt engagement metrics?
- 04
How would you test moderation tooling that must act quickly and correctly?
- 05
How would you test infinite scroll and feed performance on a low-end mobile device?
- 06
A ranking change passes offline evaluation but hurts engagement in production. How would you investigate?
- 07
Tell me about a time you owned quality for a data- or ML-driven feature.
Tips for your Reddit interview.
Be ready to test non-deterministic ranking, evaluation sets and metrics rather than exact assertions are the right framing.
Have a moderation/safety angle; protecting communities is a distinctive Reddit concern.
Lean into experimentation quality; Reddit is a heavily metrics-driven, A/B-tested product.
For mobile teams, prepare feed-performance and infinite-scroll scenarios.
Frequently Asked Questions
Does Reddit hire dedicated QA or SDET engineers?
Reddit hires quality and test engineers (including SDET-style roles) across feed, ads, safety, and platform teams, with automation and data-quality skills in demand.
How ML-focused is the interview?
It depends on the team. Feed, ranking, and ads teams probe relevance and data quality and testing non-deterministic systems; other teams focus on standard web/mobile and backend testing.
What stack should I prepare for?
Reddit runs large backend services (including Python and Go) and data systems plus iOS and Android clients. You can usually code in your strongest language; the test-architecture round is where domain reasoning matters most.
Can I practice Reddit-style questions on AssertHired?
Yes. Practice feed/ranking and data-quality test design, experimentation, and coding questions with an AI interviewer that asks follow-ups and scores your answers across four dimensions.
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