One useful fix at a time
A clear next step.
Try a three-bug starter trail. Run checks, fix a bug, then follow the next one. No signup needed.
Start small, then follow a new failure mode.
Pagination off by one
Follow a boundary error from the request to its result.
- Pagination off by one
About 10 min · No signup needed
- The Filter That Swallowed False
About 15 min · No signup needed
- Wrong Port, Right Service
About 14 min · No signup needed
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My weekly target and revisit queue
Choose your own pace.
Sign in to see your actual accepted labs against this target.
Monday–Sunday in UTC. First standard acceptances count once; revisits don’t increase this number. No streak to lose.
Revisit an earlier fix.
Sign in to revisit labs from your actual accepted history.
A review suggestion, not a skill score. Reopening a lab preserves its existing workspace.
Show how you found the fix.
Review your investigation, compare attempts and rehearse a timed round. See an example before you decide. Reports are captured from fixes accepted while Pro is active.
Debug it with a friend.
Share a free lab and compare how each of you found the cause. Both of you can run the checks and try a fix without signing up.
Season 01 · Complete at your pace
Keep the backend alive
28 focused reps and four deeper incidents. Your accepted work keeps your place.
The reviewed schedule is complete. Catch up anytime. Earlier accepted solves count. Weekly mission & rewards
Three fixes. Two days. One week.
Build permanent progress and earn rewards from accepted Practice work.
Debug the signal.
Ship the fix.
Production-shaped debugging labs across APIs, config, concurrency, and infrastructure. Reproduce the failure, follow the evidence, and prove the smallest safe change.
Try a debugging challenge without signing in. 3 guest labs are available; sign in for the full free catalogue and saved progress. Need a walkthrough? Open the guided starter.
Weekly Incident · Nov 9, 2026
One executable backend failure, a free debrief, and your next exercise.
Work-sample pack · Node.js
Backend reliability
Five multi-file investigations. A free debrief after each accepted fix. Pick up where you left off.
Choose a failure mode.
Focused bugs are targeted exercises; codebase incidents are deeper, production-shaped investigations with architecture, logs, and multiple layers. Search by symptom, then filter by lab type, source, status, or difficulty.
What are developers debugging?
Questions, dead ends, and useful investigation clues from real public Practice threads.
What developers are doing.
Recent public activity from developers who chose to share their Practice work.
More ways to practice.
Move from a focused drill to open-source history or company-style patterns when you want a different kind of debugging pressure.
Focused exercises
Train code review, system tracing, CI diagnosis, incident response, and fast debugging instincts.
Explore pathOpen-source labs
Practice against safely recreated public bug-fix history from the libraries that actually broke.
Explore pathCompany-style prep
Train backend and infrastructure failure patterns without affiliation claims.
Explore path