What is Cron?
Cron is a time-based job scheduler found in Unix and Linux operating systems. It runs tasks (called "cron jobs") automatically at specified intervals. System administrators and developers use cron for backups, log rotation, data synchronization, report generation, and any other recurring task. The schedule for each job is defined by a cron expression.
The cron daemon reads a configuration file called a crontab (cron table) that lists commands paired with their schedules. Each user can have their own crontab, and there is a system-wide crontab for administrative tasks. Modern equivalents of cron include systemd timers on Linux, launchd on macOS, Task Scheduler on Windows, and cloud-based schedulers like AWS EventBridge and Kubernetes CronJobs.
Cron Expression Fields
A standard cron expression consists of five fields separated by spaces: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). Each field supports wildcards (*), ranges (1-5), lists (1,3,5), and step values (*/10).
Common Cron Examples
* * * * * runs every minute. 0 * * * * runs at the start of every hour. 0 9 * * 1-5 runs at 9:00 AM Monday through Friday. 0 0 1 * * runs at midnight on the first day of every month. */15 * * * * runs every 15 minutes. These patterns cover the most common scheduling needs for automated tasks.
How to Use This Parser
- Enter a cron expression in the input field (five space-separated fields).
- The parser instantly explains the schedule in plain English and shows a field-by-field breakdown.
- Review the next 5 scheduled run times to verify the schedule matches your intent.
- Use the preset buttons for common schedules, or share your expression by copying the URL.
Frequently Asked Questions
What is a cron expression?
A cron expression is a string of five fields separated by spaces that defines a recurring schedule. The fields represent minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). Cron expressions are used by the Unix cron daemon and many scheduling systems to automate recurring tasks.
What does * mean in cron?
The asterisk (*) is a wildcard that means "every possible value" for that field. For example, * in the minute field means every minute, and * in the month field means every month. The expression * * * * * means "every minute of every hour of every day."
How do I run a cron job every 5 minutes?
Use the expression */5 * * * *. The */5 in the minute field means "every 5th minute" (0, 5, 10, 15, ..., 55). The asterisks in the remaining fields mean every hour, every day, every month, and every day of the week.
What is the format of a cron expression?
A standard cron expression has five fields: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6). Each field can contain a specific value, a range (1-5), a list (1,3,5), a step (*/10), or a wildcard (*). Some systems add a sixth field for seconds.
What does 0 0 * * * mean?
The expression 0 0 * * * means "at midnight (00:00) every day." The first 0 is minute 0, the second 0 is hour 0 (midnight), and the three asterisks mean every day of the month, every month, and every day of the week.
Can cron run every second?
Standard cron has a minimum granularity of one minute. It cannot natively schedule tasks at sub-minute intervals. Some extended implementations (like Kubernetes CronJobs or Quartz Scheduler) support a seconds field, but the traditional Unix cron daemon does not. For sub-minute scheduling, consider using a loop with sleep or a dedicated task scheduler.