Cron Expression Builder

A cron expression is a string of five fields (minute, hour, day of month, month, day of week) that defines a recurring schedule for automated tasks. Each field accepts specific values, ranges, step values (*/n), or an asterisk (*) meaning 'every'. For example, '0 9 * * 1-5' means 'at 9:00 AM, Monday through Friday'.

An asterisk in any field means 'every possible value' for that field. So '* * * * *' means 'every minute of every hour of every day'. A step value like '*/5' in the minute field means 'every 5 minutes' — specifically at minute 0, 5, 10, 15, and so on.

For 3:30 PM on weekdays, you would use the expression '30 15 * * 1-5'. The first field (30) is the minute, the second field (15) is the hour in 24-hour format, the asterisks mean every day and every month, and 1-5 means Monday through Friday. Days of the week range from 0 (Sunday) to 6 (Saturday).

The day-of-month field (3rd position) specifies which calendar date the job runs on, from 1 to 31. The day-of-week field (5th position) specifies which day of the week it runs, from 0 (Sunday) to 6 (Saturday). When both are set to non-wildcard values, most cron implementations run the job when either condition is true, not both — so be careful when combining these fields.

The standard Unix cron format has five fields and does not support seconds — the smallest unit is one minute. However, some platforms extend this with a 6-field format that adds a seconds field at the beginning. AWS EventBridge, Spring's @Scheduled, and Quartz Scheduler all support second-level precision with their own extended syntax.