About Cron Parser
Build cron schedules visually, read them back in plain English, and preview the next run times before you trust one in production.
What it does
Construct an expression field by field or paste an existing one, get a plain-English description, and see the actual next run times listed out. Reading the real dates is the only reliable way to catch a schedule that says something other than what you intended.
The fields, and the classic mistakes
Five fields: minute, hour, day of month, month, day of week. The most common error is */5 in the wrong column — */5 in the hours field means every five hours, not five minutes past. The second is setting both day-of-month and day-of-week, where most implementations run the job if either matches, not both. Previewing the next runs makes either mistake obvious immediately.
Common questions
- What does */5 mean?
- Every five units of whatever field it sits in — every five minutes in the first column, every five hours in the second.
- How do I run something on the last day of the month?
- With an extension: L is supported by Quartz and some others, but not by standard Unix cron. Check what your scheduler accepts.
- Which time zone do cron jobs use?
- Normally the server's local zone, which means schedules can shift with daylight saving. Many managed schedulers let you pin a zone explicitly, and it is worth doing.
- Why does my job run twice on some days?
- Usually because both day-of-month and day-of-week are set — most implementations treat that as OR, not AND.