Cron Expression Builder
Build and decode cron schedules with human-readable previews.
What is a cron expression?
A cron expression is a string of five (or six) fields separated by spaces that specifies a schedule for recurring tasks. The format was defined for the Unix cron daemon — a time-based job scheduler — and has become the standard way to express schedules in server environments, CI/CD pipelines, cloud functions, and Kubernetes CronJobs.
The five standard fields, in order, are: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where 0 and 7 both represent Sunday). Each field can be a specific value, an asterisk (*) meaning "every", a range (e.g. 1-5 for Monday to Friday), a step (e.g. */15 for every 15 minutes), or a comma-separated list (e.g. 0,6,12,18 for four times a day).
Common cron expressions: 0 * * * * (every hour), 0 0 * * * (midnight daily), 0 9 * * 1-5 (9 AM weekdays), */5 * * * * (every 5 minutes), 0 0 1 * * (1st of every month). Understanding cron is essential for DevOps, backend development, and any task that needs to run on a schedule.
Common mistakes
- Forgetting time zone — Cron runs in the server's local time zone. If your server is in UTC and users are in a different zone, scheduled tasks will run at unexpected local times.
- Day of week vs day of month confusion — Specifying both day-of-month and day-of-week as non-wildcards is an OR condition in standard cron (runs if either matches), not AND.
- Extended vs standard cron — Some tools (like AWS EventBridge, Quartz) use a 6-field format with seconds as the first field. The standard 5-field Unix cron does not include seconds.