Cron Lab

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Cron Lab reads and writes cron schedule expressions. Type one like “*/15 9-17 * * 1-5” and it tells you, in plain English, what it means, when it will run next in your timezone, and what might quietly break it.

A visual builder taps together valid expressions, or type “every weekday at 9am” and get the matching cron. One tap converts a crontab line to Quartz, Spring, AWS EventBridge, Jenkins, Kubernetes CronJob, or GitHub Actions. The schedule doctor explains why an expression never runs (February has no 30th) and flags the day-of-month and day-of-week rule that surprises almost everyone.

It works completely offline, with no ads, no tracking, and no account. Saved schedules live on your device, your whole library backs up and restores as a JSON file, and a home-screen widget shows a pinned schedule’s next run. Cron Lab is free; a one-time purchase unlocks Convert, In words, backup, and the widget.