#debugging

37 debugging interview questions, asked at Apple, Google, OpenAI and 17 more companies. Last asked Oct 2026.

Fix planted bugs in an open-source library from its failing testsCodingYou get a checkout of a real open-source library (a template engine, an HTTP client or a parser) with a few bugs planted in it. Run the test suite, follow the failures into code…
Last asked Oct 2026
+1
Find the planted bugs in a small Transformer training scriptCodingA small Transformer, its training script and some tests are provided, with a few bugs hidden in them. Find and fix them so the loss goes down and the outputs are correct, and…
Last asked Oct 2026
+1
Fix a bug in an unfamiliar repo with an AI assistantCodingYou get a small full-stack repository, a reported defect and an AI coding assistant in the browser. Reproduce the problem, find the root cause, fix it and show the fix works…
Last asked Sep 2026
Tell me about a time you dove deep to find a root causeBehavioralDescribe a hard problem you had to investigate in depth, such as an intermittent failure where the obvious metrics looked healthy. Walk through the symptom, the hypotheses you…
Last asked Sep 2026
Reconstruct call stacks from enter and exit tracesCodingA profiler gives you call stacks sampled over time, outermost frame first. Turn them into function start and end events, then go the other way: replay start/end events into stacks…
Last asked Sep 2026
Troubleshoot a crashed or unresponsive Linux serverCodingA single web server has gone down, or it is up but requests hang. Walk through how you find the cause step by step and name the exact commands you would run at each step: checking…
Last asked Sep 2026
Diagnose a slow Linux server: CPU, disk, network and logsCodingA troubleshooting round in several scenarios. For each, say which tools you reach for, what the numbers tell you and how you get from the host down to the cause. 1. CPU looks…
Last asked Sep 2026
Debug processes that crash at random while being created on Linux hostsCodingWorkloads run on a cluster of Linux servers, and some of their processes crash at random while they are being created. The interviewer has one hidden cause in mind and acts as the…
Last asked Sep 2026
Find and fix the races in a bank account classCodingYou are shown a small bank account class used from several threads, with a deposit method that loses updates. Find every concurrency bug, fix it, and explain why your fix is…
Last asked Sep 2026
Card game: pick cards that sum to 15CodingYou get a small existing codebase for a card game played with a 36-card deck, and you may use an AI assistant. The game revolves around picking cards whose values add up to 15…
Last asked Sep 2026
Recruiter screen with an AI interviewer: distributed systems experience and production debuggingBehavioralA short first screen run by an AI interviewer that asks questions quickly. Expect: 1. Your project experience with the stack in the job description (Go, Java, Spark…
Last asked Sep 2026
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Review a series of pull requestsCodingYou get two or three pull requests, each harder than the last, in Python or Java. Read each one, leave comments as you would on a real review, and point out bugs, design problems…
Last asked Aug 2026
Sharded matrix multiply: forward, backward and planted bugsCodingSplit a matrix multiplication across several devices and explain how the pieces combine. Write the forward pass and the gradient computation for that layout in NumPy or PyTorch…
Last asked Jul 2026
Debug a Python job schedulerCodingYou own a small in-process job scheduler. It runs on a fake clock so it can be tested. Users report that: - a nightly report scheduled for exactly the end of a window sometimes…
Last asked Jul 2026
Find the bugs in an AI-generated URL shortenerCodingYou are handed a URL shortener that an AI assistant wrote. Read it, find what is wrong (correctness, collisions, validation, concurrency) and fix it, explaining each problem. Only…
Last asked Jun 2026
Walk through your hardest debugging investigationBehavioralTell the story of the hardest or most memorable bug you have tracked down. Explain the symptoms, how you narrowed it down, the dead ends, the root cause and the fix, and what you…
Last asked Jun 2026
Debug an Angular UI from user reportsCodingYou get an Angular application and a handful of user bug reports. Reproduce each problem, find the cause in the code and fix it, explaining how you narrowed it down.
Last asked May 2026
Checksums, feature rollouts and dependency debuggingCodingAn online assessment in which some tasks allow an AI assistant. Reported tasks: compute checksums over input data, evaluate feature-rollout rules to decide which users get a…
Last asked Apr 2026
Root-cause a Wi-Fi chip that stops after 30 minutesCodingA Wi-Fi chip runs tests and stops sending signal after about 30 minutes. Explain how you would find the root cause. Interviewers are looking for a methodical investigation that…
Last asked Mar 2026
Find the bug in a loop conditionCodingYou are given a short Python program that does not behave as it should. Find the bug, which sits in a loop condition, explain why it causes the wrong behavior, and fix it.
Last asked Mar 2026
Debug a GRPO training script and defend the RL mathML designBelow is a small group relative policy optimization (GRPO) trainer in plain Python. The policy is a table of logits per prompt, and the reward is the share of tokens that match…
Last asked Mar 2026
Debug a shape mismatch in a PyTorch U-NetCodingA U-Net written in PyTorch fails with a tensor shape mismatch. Find the cause (typically where skip connections are concatenated with upsampled features whose size no longer…
Last asked Mar 2026
Debug a staged C++ project with AI tools allowedCodingA C++ program is split into stages, each hiding a logic error, a memory bug or a race. Run it, observe the output, and fix each stage, using an AI assistant if you like while…
Last asked Feb 2026
Owning and debugging infrastructure modulesBehavioralFor a storage or infrastructure role: describe a module you owned end to end, a hard production problem you debugged in it, how you found the root cause, and what you changed so…
Last asked Jan 2026
Find the conflicting pair of tests with a black-box runnerCodingA black-box run(tests) runs a set of tests together and reports failure when the set contains a conflicting pair of tests; any test alone passes. Find the conflicting pair with as…
Last asked Jan 2026
Debug a project-assignment codebaseCodingYou get a small codebase spread over several files that assigns projects (for example to students or courses). Some tests fail. Read your way around it under time pressure, find…
Last asked Jan 2026
Debug performance problems in a distributed systemSystem designA distributed service has become slow. Walk through how you find out why: metrics, tracing and logs, finding the slow component, common causes (hot partitions, lock contention…
Last asked Dec 2025
Debug a vision transformer notebookCodingA notebook trains a small vision transformer on handwritten digits but performs badly. Find and fix the implementation bugs, paying attention to details like masking and padding…
Last asked Oct 2025
Write a text parser and fix the bugs in an ML projectCodingIn a one-hour round on an existing ML project: first write a parser that turns raw text data into the format the project needs, then find and fix three bugs elsewhere in a fairly…
Last asked Sep 2025
Troubleshoot high CPU, slow responses and DNS failuresCodingA production service shows high CPU, rising latency, and some requests failing on name resolution. Explain step by step how you investigate each: the tools and commands you would…
Last asked Sep 2025
Diagnose inconsistent data in a distributed databaseSystem designUsers report reading different values for the same record from a replicated database. How do you find the cause? Go through replication lag, read and write consistency settings…
Last asked Sep 2025
Debug an overloaded Kubernetes clusterSystem designAn infrastructure round: a service running on Kubernetes is overloaded. Say which metrics you want to see first; the interviewer draws them for you, and you narrow the cause down…
Last asked Aug 2025
Python practicals: debug async code, find files by pattern, read nested JSONCodingA set of short practical Python tasks: 1. Read a helper class that keeps pulling data from a response and writing it out, and explain what it is for. 2. Debug a piece of…
Last asked Aug 2025
Debug a model whose accuracy drops after deploymentML designA model that looked fine offline loses accuracy suddenly once it is in production. Walk through how you would debug the whole pipeline step by step: where you look first, how you…
Last asked Aug 2025
Find bugs and slow renders in a React appCodingYou get a small React codebase with several bugs and performance problems. Find and fix them: unnecessary re-renders, event listeners that are never cleaned up, and similar…
Last asked Aug 2025
Diagnose a data pipeline's quality and performance problemsBehavioralAsked in a hiring-manager conversation for a solutions architect role: how do you diagnose a data pipeline whose output has quality problems, or whose runs have become slow? Walk…
Last asked Jul 2025
Debug a codebase then propose long-term fixesCodingYou inherit a small order service: an inventory that holds stock for orders, a pricing module, and the order service that ties them together. Support tickets say stock…