Code Room
Practice the whole technical round. Coding, system design, code review, and on-call — drilled by level, role, and subject, run against tests in the browser, and graded by a coach, not a judge.
Built for Computer games IT services Software development Technology Telecom
Coding Write, debug, and run code against tests — narrated. System design Design an architecture, clarify, scale, trade off. Code review Read a diff — find the bug, the smell, the risk. On-call Diagnose an incident, mitigate, write the postmortem. Vibe coding Direct an AI to build it — then catch what it got wrong.
Filters
Interview domain
Code quality & review Concurrency Security Algorithms & data structures Databases & SQL Networking & APIs Distributed systems Reliability & on-call Storage & CDN ML systems
Subject
Correctness Security Error handling Performance Concurrency Ai generated code Xss Unnecessary allocation Repeated work Swallowed exceptions
Show more Language
Any Go Java Python Javascript
Code review Easy
Review this helper meant to return events from the last n days. What do you flag?
cr-p001 Correctness · Mid–Senior · ~18 min · Code quality & review
Code review Hard
This account-debit code runs in a multi-threaded server. What's wrong?
cr-p002 Concurrency · Mid–Senior · ~18 min · Concurrency
Code review Hard
Review this endpoint handler.
cr-p003 Security · Mid–Senior · ~18 min · Security
Code review Medium
Review this 'download invoice' handler.
cr-p004 Security · Mid–Senior · ~18 min · Security
Code review Medium
Review this code that builds an order summary.
cr-p005 Performance · Mid–Senior · ~18 min · Code quality & review
Code review Easy
Review this dedup-and-preserve-order function.
cr-p006 Performance · Mid–Senior · ~18 min · Code quality & review
Code review Easy
Review this payment retry wrapper.
cr-p007 Error handling · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this file-processing function.
cr-p008 Error handling · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this API change. The endpoint used to return 404 for a missing user; the PR changes it to:
cr-p009 Api contract · Mid–Senior · ~18 min · Networking & APIs
Code review Medium
Review this helper.
cr-p010 Readability · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this unit test.
cr-p011 Test coverage · Mid–Senior · ~18 min · Code quality & review
Code review Medium
An AI assistant produced this 'merge two sorted lists' function. It passed a couple of examples. Review it.
cr-p012 Ai generated code · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this config + login code.
cr-p013 Security · Mid–Senior · ~18 min · Security
Code review Medium
Review this pricing code (prices are dollar amounts as floats).
cr-p014 Correctness · Senior–Staff · ~18 min · Code quality & review
Code review Medium
Review this view-counter used across many web workers.
cr-p015 Concurrency · Mid–Senior · ~18 min · Concurrency
Code review Easy
Review this code.
cr-p016 Null handling · Entry–Mid · ~18 min · Code quality & review
Code review Hard
Review this code that trusts a third-party webhook payload.
cr-p017 Security · Senior–Staff · ~18 min · Security
Code review Medium
Review this export endpoint.
cr-p018 Performance · Senior–Staff · ~18 min · Code quality & review
Code review Medium
Review this front-end code rendering a comment.
cr-p019 Security · Mid–Senior · ~18 min · Security
Code review Easy
Review this Python function.
cr-p020 Correctness · Entry–Mid · ~18 min · Code quality & review
Code review Medium
Review this new list endpoint.
cr-p021 Api contract · Mid–Senior · ~18 min · Networking & APIs
Code review Hard
Review this retry loop calling a payment provider.
cr-p022 Error handling · Senior–Staff · ~18 min · Code quality & review
Code review Medium
Review this code that decides if a subscription expired.
cr-p023 Correctness · Mid–Senior · ~18 min · Code quality & review
Code review Hard
Review this password-reset token generator.
cr-p024 Security · Senior–Staff · ~18 min · Security
Code review Medium
An AI wrote this function to compute the median of a list. Review it before merging.
cr-p025 Ai generated code · Mid–Senior · ~18 min · Code quality & review
Code review Hard
Review this lazily-initialized singleton used from multiple threads.
cr-p026 Concurrency · Senior · ~18 min · Concurrency
Code review Medium
Review this file-download handler.
cr-p027 Security · Mid–Senior · ~18 min · Security
Code review Medium
Review this function that sums a possibly deeply-nested list.
cr-p028 Correctness · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this update-profile handler.
cr-p029 Security · Mid–Senior · ~18 min · Security
Code review Medium
Review this caching addition.
cr-p030 Caching · Mid–Senior · ~18 min · Distributed systems
Code review Medium
Review this 'create a file only if it doesn't exist' code.
cr-p031 Concurrency · Mid–Senior · ~18 min · Concurrency
Code review Easy
Review this function.
cr-p032 Correctness · Entry–Mid · ~18 min · Code quality & review
Code review Easy
Review this code added to a hot request path.
cr-p033 Performance · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this exception handling.
cr-p034 Error handling · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this code that checks whether a balance is paid off.
cr-p035 Correctness · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this code that removes inactive users.
cr-p036 Correctness · Mid–Senior · ~18 min · Code quality & review
Code review Medium
Review this CORS configuration on an API that uses cookie auth.
cr-p037 Security · Mid–Senior · ~18 min · Security
Code review Hard
Review this transfer code.
cr-p038 Correctness · Senior · ~18 min · Code quality & review
Code review Hard
Review this input validation.
cr-p039 Security · Senior · ~18 min · Security
Code review Easy
Review this code that waits for a job to finish.
cr-p040 Performance · Mid–Senior · ~18 min · Code quality & review
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