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Cron expression builder

Linux crontab uses five fields: minute, hour, day of month, month, and day of week. Paste a line, or build one from the fields and presets.

Expression Five fields, or a shortcut such as @daily. @reboot is explained but has no next run times.

Minute0–59 Hour0–23 Day of month1–31 Month1–12 or JAN Day of week0–7 or MON; 0 and 7 are Sunday

Normalized expression

0 3 * * *

The crontab line uses a placeholder command. Replace it with your script and an absolute path.

Explanation

Next eight runs

How to use this on a small VPS

On most Debian or Ubuntu machines the file you want is the current user's crontab (crontab -e), not a random file in /etc. Use 24-hour times, write the command with an absolute path, and send output somewhere size-capped — a job that appends forever will fill a 1 GB disk.

This builder follows Vixie cron rules, which is what you get with a normal Linux crontab. If both day-of-month and day-of-week are restricted, the job runs when either field matches. systemd timers, Kubernetes CronJobs, and Java “Quartz” expressions can look similar but do not always mean the same thing — this tool will refuse 6- and 7-field lines so you do not copy the wrong dialect onto the server.

A job every minute is fine for a tiny health check; it is a bad idea for backups, apt upgrade, or anything that spikes memory. Prefer nice and ionice for heavy work, and pick a quiet hour.