What is a cron expression?

A cron expression is a string of five (or six) fields that defines a recurring schedule. The standard five fields 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 are Sunday). Special characters include * (any value), , (list), - (range), and / (step). For example, */15 * * * * runs every 15 minutes.

# Cron expression format:
# ┌───── minute (0-59)
# │ ┌───── hour (0-23)
# │ │ ┌───── day of month (1-31)
# │ │ │ ┌───── month (1-12)
# │ │ │ │ ┌───── day of week (0-7, Sun=0 or 7)
# │ │ │ │ │
# * * * * *  command

# Special characters:
# *    any value         */5  every 5 units
# ,    list (1,3,5)      -    range (1-5)
# @hourly   = 0 * * * *
# @daily    = 0 0 * * *
# @weekly   = 0 0 * * 0
# @monthly  = 0 0 1 * *

Common use cases

Cron expressions schedule automated backups, log rotation, report generation, database maintenance, email digests, and deployment pipelines. They are used in Unix crontab, Kubernetes CronJobs, GitHub Actions, AWS EventBridge, and CI/CD platforms. Understanding the syntax is essential for any developer working with scheduled automation.