New challenge every day

Daily Developer Debug

One practical bug, API behavior, or security decision. Choose an answer, read the reasoning, and build a local streak—no signup required.

Challenge

#286

Next puzzle

--:--:--

Data Intermediate

A CSV identifier lost its zero

Why should a CSV-to-JSON converter preserve "00123" as text in many imports?

Read carefully

account_id,name
00123,Ada

Choose one answer

Your local progress

day streak

solved

Progress is stored only in this browser. Clearing browser storage resets it.

How it works

1Read the small reproducible example.
2Choose the behavior or fix you would trust.
3Review the explanation and apply the takeaway.

Challenge a teammate

Share your result without revealing the correct answer.

Why practice debugging?

Writing code and reviewing code are different skills. Short debugging exercises help developers slow down, predict behavior, recognize unsafe assumptions, and select tests that distinguish a correct implementation from a plausible-looking mistake. These challenges are educational examples—not a substitute for your language runtime, project tests, official specifications, or security review.