Parse any 5-field cron expression into a human-readable schedule, see the next 10 run times, and build expressions visually. Everything runs in your browser.

Understanding Cron Expressions: A Complete Guide

A cron expression is a compact string of five space-separated fields that defines a recurring schedule. Originally created for the Unix cron daemon in the 1970s, cron expressions are now the universal language for scheduling tasks across operating systems, cloud platforms, CI/CD pipelines, container orchestrators, and web application frameworks. If you have ever set up an automated backup, a recurring email, or a periodic database cleanup, chances are a cron expression was involved.

The standard five-field format is minute hour day-of-month month day-of-week. Each field accepts specific values, ranges, lists, wildcards, and step intervals. Together they describe exactly when a job should run — from once a minute to once a year and everything in between.

The Five Fields Explained

The minute field (0–59) controls which minute of the hour the job fires. Setting it to 0 means the top of the hour; */15 means every 15 minutes. The hour field (0–23) uses 24-hour time: 0 is midnight and 13 is 1 PM. The day-of-month field (1–31) selects specific calendar dates. The month field (1–12 or JAN–DEC) restricts execution to certain months. The day-of-week field (0–7 or SUN–SAT, where both 0 and 7 represent Sunday) targets specific weekdays.

Special Characters and Syntax

The asterisk (*) means "every possible value" — * in the hour field matches hours 0 through 23. A comma creates a list: 1,3,5 in the day-of-week field matches Monday, Wednesday, and Friday. A hyphen defines a range: 9-17 in the hour field means 9 AM through 5 PM. A slash specifies step intervals: */10 in the minute field fires at 0, 10, 20, 30, 40, and 50 minutes past each hour. You can also combine a range with a step, such as 1-5/2 in the day-of-week field, which matches Monday, Wednesday, and Friday.

Common Cron Expressions

* * * * * — every minute
0 * * * * — every hour on the hour
0 0 * * * — once a day at midnight
0 9 * * 1-5 — weekdays at 9 AM
0 0 1 * * — first day of every month at midnight
*/5 * * * * — every 5 minutes
0 0 * * 0 — every Sunday at midnight
0 0 1 1 * — once a year on January 1st at midnight

How Day-of-Month and Day-of-Week Interact

A subtlety that trips up many users: when both day-of-month and day-of-week are set to non-wildcard values, traditional cron implementations use a union (OR) — the job runs if either condition is met. For example, 0 0 15 * 5 runs at midnight on the 15th of every month and every Friday, not only on Fridays that fall on the 15th. When one of the two fields is *, the other field alone determines matching days.

Frequently Asked Questions

What is crontab?
crontab is the Unix command used to create, edit, and manage cron job schedules. Each user on a Unix system can have their own crontab file, and the cron daemon reads these files to execute jobs on schedule.

What is the difference between 5-field and 6-field cron?
The standard cron format has 5 fields (minute through day-of-week). Some systems like Spring and Quartz add a seconds field at the beginning, creating a 6-field format. This tool parses the standard 5-field format, which is the most widely used.

Can I use names instead of numbers?
Yes. The month field accepts three-letter abbreviations (JAN through DEC) and the day-of-week field accepts SUN through SAT. Names are case-insensitive and can be used in ranges, such as MON-FRI.

How do I test a cron expression?
Paste your expression into the input field above. This parser instantly shows a plain-English description, a breakdown of each field, and the next 10 scheduled execution times based on your current local time. Everything runs client-side in your browser — no data is sent to any server.

Bookmark this cron expression parser for quick reference whenever you need to write, debug, or verify a cron schedule. It's free, private, and works entirely in your browser.