Cron Expression Parser

Cron expressions are compact scheduling strings used by servers, CI jobs, automation platforms, and maintenance scripts. They are powerful, but a small typo can change a task from daily to every minute, or from weekdays to weekends.

This parser explains a Unix 5-field cron expression in plain language, breaks down each field, and shows upcoming run times using the timezone you choose in the tool.

The v1 parser supports standard Unix cron with five fields:

minute hour day-of-month month day-of-week

• Minute values from 0 to 59.
• Hour values from 0 to 23.
• Day-of-month values from 1 to 31.
• Month values from 1 to 12, plus names such as JAN and DEC.
• Day-of-week values from 0 to 7, plus names such as MON and FRI. Both 0 and 7 mean Sunday.

It supports wildcards, comma lists, ranges, and step values such as */15 or 9-17/2.

Cron dialects are not universal. Quartz, systemd timers, cloud schedulers, Kubernetes, GitHub Actions, and hosting platforms can add their own fields or special operators.

• Seconds fields and year fields are not parsed as Unix cron.
• Quartz operators such as ?, L, W, and # are reported as unsupported.
• Macros such as @daily and @reboot are not expanded.
• Command text after a schedule is not treated as part of the expression.

A cron expression does not include a timezone by itself. The same expression can run at different moments depending on whether the server uses UTC, a local system timezone, or a scheduler-specific timezone setting.

• The preview shows run times in the selected IANA timezone and in UTC.
• Spring-forward transitions can skip local wall-clock times that do not exist.
• Fall-back transitions can repeat a local wall-clock time; scheduler behavior may differ.
• If both day-of-month and day-of-week are restricted, Unix cron commonly uses OR semantics.

For critical jobs, treat the preview as a planning aid and confirm behavior in the scheduler itself.