Cron Expression Explainer

What is a Cron Expression?

A cron expression is a compact string that describes a recurring schedule. Originally used in Unix-like operating systems to automate tasks via the cron daemon, cron expressions are now used everywhere — from CI/CD pipelines and cloud functions to Kubernetes jobs and monitoring systems.

A standard cron expression has five fields separated by spaces: minute, hour, day of month, month, and day of week. Some systems add a sixth seconds field at the beginning. Each field accepts specific values, wildcards, ranges, and intervals.

Cron Syntax Reference

Special Characters

• * — matches every possible value ("any")
• , — list separator: 1,3,5 means values 1, 3, and 5
• - — range: 1-5 means values 1 through 5
• / — step: */5 means every 5th value; 10-30/5 means every 5th value from 10 to 30

How to Read a Cron Expression

Read a cron expression from left to right, one field at a time:

1. Minute — what minute of the hour does it run?
2. Hour — what hour of the day?
3. Day of Month — which day(s) of the month?
4. Month — which month(s)?
5. Day of Week — which day(s) of the week?

For example, 30 9 * * 1-5 reads as: "At minute 30, at 9 AM, every day of month, every month, Monday through Friday" — or simply "weekdays at 9:30 AM".

Common Cron Expression Examples

• * * * * * — every minute
• 0 * * * * — at the start of every hour
• 0 0 * * * — every day at midnight
• 0 9 * * 1-5 — weekdays at 9:00 AM
• */5 * * * * — every 5 minutes
• */15 * * * * — every 15 minutes
• 0 0 * * 0 — every Sunday at midnight
• 0 0 1 * * — first day of every month at midnight
• 0 0 1 1 * — every January 1st at midnight (yearly)
• 0 */6 * * * — every 6 hours
• 0 8,17 * * 1-5 — weekdays at 8 AM and 5 PM

What's the Difference Between 5-Field and 6-Field Cron?

The standard cron format has 5 fields: minute, hour, day of month, month, day of week. This is what you'll find in Linux crontab, GitHub Actions, and most scheduling tools.

Some systems (Spring, Quartz, and certain cloud platforms) use a 6-field format that adds a seconds field at the beginning: seconds, minute, hour, day of month, month, day of week.

This tool auto-detects which format you're using based on the number of fields. If your expression has 6 space-separated parts, it's treated as a 6-field expression with seconds.