Cron Expression Generator

What Cron Is

Cron is the job scheduler that has shipped with Unix systems for decades. You hand it an expression that describes when something should run, and it runs that thing on exactly that schedule, forever, without you thinking about it again. A cron expression is five fields separated by spaces, and each field controls one part of the timing.

The Special Characters

Four symbols do most of the work inside those five fields. An asterisk means every value, so an asterisk in the hour field means every hour. A comma builds a list, so 1,15,30 in the minute field fires at three specific minutes. A hyphen makes a range, so 1-5 in the day-of-week field covers Monday to Friday. A slash sets a step, so */15 in the minute field means every fifteenth minute starting from zero.

Common expressions

The Day-of-Month vs Day-of-Week Gotcha

Here is the trap that surprises almost everyone. When you set both the day-of-month field and the day-of-week field to real values, most cron implementations run the job when either one matches, not when both do. So "0 0 13 * 5" does not mean the 13th only if it is a Friday; it means every 13th and every Friday. If you actually need both conditions to line up, you generally have to check the date inside the script itself.

Cron syntax reaches well past the original Unix crontab now. You will find the same five fields in CI pipeline schedules, GitHub Actions workflows, Kubernetes CronJobs, and the managed schedulers in every major cloud. Learn it once and the knowledge travels everywhere.

The generator above builds and explains expressions right in your browser, translating each field into plain English as you go so you can trust what you are about to schedule.