Refactor Challenge
Read a buggy snippet. Predict the FIRST thing a senior reviewer would flag. Then reveal Lambda's senior-grade review and check yourself.
Sibling tools: paste your own code at ✨ Refactor Coach, PR-review-style at ⚔️ Diff Battle, or read an incident replay at 🔥 Postmortem Replay.
O(n²) lookup loop
A function that fetches users by id. Works on a small test list. What does a senior flag FIRST?
Start the challenge →Bare except + mutable default
Looks defensive. Has TWO production-grade bugs hiding in five lines. What's the worst?
Start the challenge →Class with no encapsulation
Everything public, no validation. What would a senior flag FIRST in a payments-domain review?
Start the challenge →Timezone-naive datetime
A user store that records signup timestamps. Works on the dev machine. What does a senior flag FIRST in the PR?
Start the challenge →O(n²) string concatenation
A CSV renderer that builds the output with `+=`. Looks fine; runs slow on a 100k-row job. What does a senior flag FIRST?
Start the challenge →More challenges added as the curriculum grows. Got a snippet you want turned into a challenge? Email us.