With just a little practice you can write a crontab from memory faster than with this tool, but making the tool is the real exercise. You really know something when you know it well enough to teach it to a human or a machine.

Use * for every. Enter a singe number (n) or range (n-n).



* * * * * command
- – – – -
| | | | |
| | | | +—– Day of week (0–7) (Sunday=0 or 7) or Sun, Mon, Tue,…
| | | +———- Month (1–12) or Jan, Feb,…
| | +————-— Day of month (1–31)
| +——————– Hour (0–23)
+————————- Minute (0–59)

crontab [ -u user ] { -l | -r | -e }

List current crontab.

crontab -u user -l

Remove current crontab.

crontab -u user -r

Edit current crontab.

crontab -u user -e

Further Reading:
https://ss64.com/bash/crontab.html
https://en.wikipedia.org/wiki/Cron
https://hull1.com/cron/