What is a cron expression?
A cron expression is a string of five fields that defines a recurring schedule on Unix-based systems. Each field represents a unit of time, and together they describe exactly when a job should run — every minute, every weekday at 9 AM, the first of every month, and so on.
The name comes from chronos (Greek for time). The cron daemon reads a crontab file and executes commands at the scheduled times.
Anatomy of a cron expression
A standard cron expression has exactly 5 fields, separated by spaces:
09**1-5# every weekday at 9:00 AMSpecial characters
*Any value* * * * * — every minute,List0 9,17 * * * — 9 AM and 5 PM daily-Range0 9 * * 1-5 — weekdays at 9 AM/Step*/15 * * * * — every 15 minutesCommon examples
Every minute / hour
* * * * *Every minute*/5 * * * *Every 5 minutes*/15 * * * *Every 15 minutes*/30 * * * *Every 30 minutes0 * * * *Every hour, on the hour0 */2 * * *Every 2 hoursDaily
0 0 * * *Every day at midnight0 6 * * *Every day at 6:00 AM0 9 * * *Every day at 9:00 AM30 23 * * *Every day at 11:30 PM0 8-18 * * *Every hour from 8 AM to 6 PMWeekdays / weekends
0 9 * * 1-5Every weekday (Mon–Fri) at 9:00 AM0 0 * * 6,0Saturday and Sunday at midnight*/5 9-17 * * 1-5Every 5 min during business hours (weekdays)0 8 * * 1Every Monday at 8:00 AM0 17 * * 5Every Friday at 5:00 PMWeekly / monthly
0 0 * * 0Every Sunday at midnight0 0 1 * *First day of every month at midnight0 0 L * *Last day of every month (extended cron only)30 4 1,15 * *4:30 AM on the 1st and 15th of each month0 0 1 */3 *First day of every quarter (Jan, Apr, Jul, Oct)Yearly
0 0 1 1 *January 1st at midnight (once a year)0 0 25 12 *December 25th at midnight0 9 1 1 *New Year's Day at 9:00 AMExtended cron (6 fields)
Some platforms add a seconds field at the beginning, giving 6 fields total. Standard Unix cron has a 1-minute minimum resolution — the seconds field is non-standard.
0/30 * * * * ? # every 30 seconds (Quartz syntax)Always check which format your platform expects. Tools like Kubernetes CronJobs use standard 5-field cron. GitHub Actions workflows and AWS EventBridge use their own extended syntax.