Cron Syntax Explained

A cron expression consists of five fields separated by spaces: minute hour day-of-month month day-of-week. Each field accepts specific values, wildcards (*), ranges (1-5), steps (*/5), and comma-separated lists (1,3,5).

The five fields and their valid ranges are: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). A wildcard * means "every possible value." A step like */5 means "every 5th value starting from the minimum." A range like 9-17 means "9 through 17 inclusive."

These building blocks combine to create powerful schedules. For example, 30 9 1,15 * * means "at 9:30 AM on the 1st and 15th of every month." Understanding the syntax lets you write any schedule without relying on a generator — though tools like SimpleCronTab make it faster and less error-prone.