About the Cron Expression Builder
Cron's five-field syntax is compact and merciless: a transposed field silently changes "every day at 3" into "every minute during 3 o'clock". This builder constructs expressions from visual selections and translates any expression into plain language, so you can verify intent before deploying.
It covers the practical variants — standard five-field cron, ranges, steps (*/15), lists, and the day-of-week vs day-of-month interaction that is cron's most misunderstood behavior.
Frequently asked questions
Why did my cron job run more often than expected?
The classic: 0 3 * * * runs daily at 03:00, but * 3 * * * runs every minute from 03:00–03:59. The other trap is day-of-month and day-of-week together — in standard cron they are OR'd, not AND'd: 0 0 1 * 1 runs on the 1st AND every Monday, not only Mondays-the-1st.
How do timezones and DST affect cron schedules?
Classic cron runs in the system timezone: a 02:30 job may run twice or never on DST transition nights. Kubernetes CronJobs default to the kube-controller-manager's timezone unless you set the timeZone field (stable since 1.27). For anything time-sensitive, schedule in UTC and convert deliberately.
What is the difference between cron in crontab, Kubernetes, and Quartz?
Crontab uses five fields (minute through day-of-week). Kubernetes CronJobs use the same five-field syntax plus optional time zones. Quartz (Java) uses six or seven fields including seconds and requires ? in one of the day fields — pasting a Quartz expression into crontab, or vice versa, fails or silently misschedules.
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