What is a cron expression?
A cron expression is a string made up of five fields separated by spaces that specifies a schedule for recurring tasks. The format comes from the Unix cron daemon, which has been scheduling automated jobs since the 1970s. Today cron syntax is used in Linux/macOS crontabs, GitHub Actions, AWS EventBridge, Kubernetes CronJobs, and many other scheduling systems.
Cron syntax explained
Each of the five fields represents a unit of time: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where both 0 and 7 represent Sunday). An asterisk * means "every value". A slash / means "every N" (e.g. */5 in the minute field means every 5 minutes). A comma separates multiple values, and a hyphen defines a range.
Common cron schedule examples
0 9 * * 1-5 — every weekday at 9 AM. */15 * * * * — every 15 minutes. 0 0 1 * * — midnight on the first of every month. 0 12 * * 0 — every Sunday at noon. 30 6 * * * — every day at 6:30 AM. These patterns cover the vast majority of real-world scheduling needs.
Use cases for cron jobs
Cron jobs are ideal for database backups, sending scheduled emails or reports, clearing temporary files, running data sync processes, refreshing caches, triggering CI/CD pipelines, and polling external APIs. Any task that should happen on a fixed schedule — rather than in response to a user action — is a good candidate for a cron job.