Practical Round
Read code someone else wrote and find what's wrong: a pull request with a race condition, a failing test, or a slow endpoint. A growing number of companies use this round in place of an algorithm puzzle.
Start a Session
Set a level to tune the cards. Cards you rated Shaky come up more often.
How It's Graded at Each Level
- Junior
Find the bug the failing test points at, fix it, and explain the fix.
- Mid
Spot the correctness issues in a review, rank them, and suggest a concrete change for each.
- Senior
Catch the race, the N+1 query, and the security hole, and say which one blocks the merge.
- Staff
Review for the system around the diff: rollout risk, observability, and what breaks downstream.
- Principal
Seldom asked. When it is, the bar is judgment on what to fix now and what to schedule.
Drill Types
- Code ReviewFind the race, the N+1 query, or the injection in thirty lines.3 to 5 min a review
- DebuggingA function and a failing test. Find the bug.3 to 5 min a bug
- PR Review LabReview a full pull request, mark each comment by severity, and give a verdict.25 to 30 min a PR
- AI-Assisted Coding LabBuild a feature with an assistant whose suggestions are sometimes wrong.45 min a task
Read These First
All Library Pages- GuideCode Review ReferenceGuide
- GuideDebugging ReferenceGuide
- TechniqueOptimistic ConcurrencyTechnique
- GuideSecurity ReferenceGuide
Common Mistakes
Nitpicking style first
Lead with what breaks in production. Naming and formatting come last.
Fixing before reproducing
Say what input triggers the bug before you change a line.
No severity
Mark what blocks the merge and what can wait, so the author knows where to start.
Matching Mock
Mixed Timed Drill
A timed set of cards from several rounds, with a report at the end.