Labs · 87 puzzles

Small problems, real checkers.

Checked by the same regex engine, cron parser and SQL engine the tools run. Progress stays in this browser — no account, no leaderboard.

28holes

Regex GolfWrite the shortest regular expression that matches every string on one list and none on the other. Twenty-eight holes, scored against par, checked in your browser.

0 of 28 solved on this device

Start at puzzle 1

28puzzles

Cron PuzzlesTwenty-eight schedules described in words; write the five-field cron expression that fires at exactly those times, checked by the site's own cron parser.

0 of 28 solved on this device

Start at puzzle 1

31puzzles

Data Wrangling in SQLThirty-one puzzles: small tables in, an exact result set out. Written in SQL, run on DuckDB in your browser, compared cell by cell.

0 of 31 solved on this device

Start at puzzle 1

What a lab is, and is not

A lab is a set of small, self-contained problems with a checker. The checker is the point: it is the regex engine, the cron parser and the SQL engine the tools already run, so a solution that passes here behaves the same way in the tool and in your own code. Reference solutions exist for every puzzle and are executed in the site's test suite, so a puzzle cannot be broken without a test failing.

Progress is kept in this browser and nowhere else: solved puzzles, best scores, a streak of days with at least one solve. There is no account, no leaderboard and no name attached to a result, because a leaderboard needs an identity and this site does not keep any. A solve can be shared as a link that says which puzzle and what score, which is all a badge needs to say.

There are no JavaScript puzzles. Running someone else's code needs an evaluator the site's security policy does not permit, and the three languages here give the same satisfaction without executing anything but a pattern, a schedule or a query.