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learn by doing

Practice like it's production — without the risk.

Leaderboard

Every challenge is an isolated sandbox. You fix real bugs, review real PRs, and write real tests. Nothing leaves the playground.

Points, streaks and a place on the board. Sign in to start counting — progress is tracked from your first completion.

starting line

Your first branch starts here.

6 challenges. Each one drops you into a real repository — no theory, just the workflow. We suggest starting with something gentle.

The load-more button that never stops

Bug Fix15 min
Start first challenge
Code Review
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Review a noisy pull request

A 380-line PR bundles a real fix with unrelated churn and a breaking contract change. Review like a maintainer: keep what belongs, flag what doesn't.

moderate20 min
Bug Fix
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Fix the broken EventEmitter

Listeners keep firing after off() is called. A real-time dashboard is receiving phantom updates from events it explicitly unsubscribed from — find out why and fix it.

moderate20 min
Not started

The load-more button that never stops

A paginated feed keeps showing 'Load more' even on the last page — triggering an extra empty fetch on every visit. The data is correct, but the metadata lies.

beginner15 min
Testing
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Write tests for fetchUpstream

The timeout fix landed but nothing proves it. Write the tests that lock in the new behavior before it can quietly regress.

moderate18 min
Git
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Resolve a three-way merge conflict

Two branches both modified the same auth module. Reconcile all three conflicts without dropping either branch's intent — and figure out when neither side is the right answer.

demanding25 min
Documentation
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Document the gateway module

fetchUpstream has no docs, no examples, and a non-obvious null return. Write the documentation that the next contributor needs before they can use it safely.

beginner15 min
Badges
First Merge
Review Corps
Coverage Hero
Ship It
Doc Writer
7-Day Streak
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Complete challenges to unlock badges. Each one marks a skill earned, not just a box ticked.

Learning pathsSee all
Code Review

The life of a breaking change

A null enters a codebase hidden inside a 380-line PR. Follow it: catch it in review, work out who it breaks, pin it down with tests, and document it before it catches the next person.

2 guides · 3 challenges