What Is a Cron Expression?
Cron expressions define recurring schedules using a compact five-field syntax: minute, hour, day-of-month, month, and day-of-week. They power scheduled tasks in Unix/Linux systems, CI/CD pipelines (GitHub Actions, GitLab CI), cloud services (AWS CloudWatch, Google Cloud Scheduler), and job queues. This builder lets you construct cron expressions visually and see the next execution times.
Cron Syntax Quick Reference
* = every value. */n = every n units. n-m = range from n to m. n,m = specific values n and m. Fields in order: minute (0-59), hour (0-23), day (1-31), month (1-12), weekday (0-6, where 0 = Sunday).
How to Use This Cron Builder
- Select the frequency — Choose how often the job should run — every minute, hourly, daily, weekly, monthly, or custom.
- Configure the schedule — Set the specific minute, hour, day of month, month, and day of week for your cron job.
- Read the expression — The tool displays the 5-field cron expression with a human-readable description of when it will run.
- View the next run times — Check the next 5 scheduled execution times to verify the expression does what you expect.
- Copy the expression — Grab the cron expression for your crontab, CI/CD pipeline, or scheduled task configuration.
Tips and Best Practices
- → Know the five fields. Left to right: minute (0–59), hour (0–23), day of month (1–31), month (1–12), day of week (0–7, where 0 and 7 are Sunday).
- → Use * for 'every' and */n for intervals.
*/5 * * * * means every 5 minutes. 0 */2 * * * means every 2 hours on the hour.
- → Be careful with day-of-month and day-of-week. When both are set (not *), most cron implementations run the job when EITHER condition is true — not when both are true. This catches many beginners off guard.
- → Avoid scheduling at midnight. Many cron jobs are scheduled at 0 0 * * * (midnight). Spread your jobs across different times to avoid resource contention on servers.
Frequently Asked Questions
What is a cron expression?
A five-field string defining a schedule: minute, hour, day of month, month, day of week. Example: '0 9 * * 1' = 9 AM every Monday. Used in Unix, CI/CD, and cloud schedulers.
What does * mean in cron?
Asterisk means 'every' or 'any value.' */5 means every 5 units, 1-5 means range 1 through 5.
How do I run a job daily?
'0 0 * * *' runs at midnight daily. '0 9 * * *' runs at 9 AM daily. First field = minute, second = hour, asterisks = every day/month/weekday.
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, hour, day of month, month, and day of week. Cron is used by Unix/Linux systems, CI/CD platforms (GitHub Actions, GitLab CI), cloud schedulers (AWS CloudWatch, Google Cloud Scheduler), and task automation tools.
What does the cron expression '0 9 * * 1-5' mean?+
It means 'at 9:00 AM, Monday through Friday.' Breaking it down: 0 (minute 0), 9 (9th hour / 9 AM), * (every day of the month), * (every month), 1-5 (Monday through Friday). This is a common schedule for business-hours tasks.
How do I test a cron expression?+
Use a cron expression tool like this one to see the next scheduled run times. You can also test in a terminal with crontab -e to add a temporary job that writes to a log file, then watch the log to verify timing.
How do I schedule a cron job to run daily?+
Use '0 0 * * *' to run at midnight every day, or '0 9 * * *' for 9 AM daily. The first field is minute (0), second is hour (0 or 9), and the three asterisks mean every day of month, every month, every day of week.
How do cron expressions handle daylight saving time?+
Classic Unix cron runs jobs in the server's local timezone, so on the spring-forward day a job scheduled for 2:30 AM is skipped and on the fall-back day it runs twice. Modern schedulers like systemd timers and cloud cron services (AWS EventBridge, Vercel Cron) typically run in UTC by default to avoid the issue. For jobs that must run exactly once per day, schedule them in UTC, not local time.
What is the difference between a step value and a list in cron?+
Lists run on the exact values you specify (0,15,30,45 means top of hour and quarter past, half past, and quarter to). Steps run on a regular interval starting from the range start (*/15 means every 15 minutes starting at 0, which lands on the same minutes for hours but works for any interval). Use a list when you need irregular times, a step when you want a regular cadence — they are interchangeable for simple cases but step expressions are shorter and clearer.
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