Cron expression generator

Reembun. (2026, July 28). Cron expression generator. https://reembun.com/cron-generator

The five fields

┌───────────── minute (0-59)
│ ┌─────────── hour (0-23)
│ │ ┌───────── day of month (1-31)
│ │ │ ┌─────── month (1-12)
│ │ │ │ ┌───── day of week (0-6, Sunday = 0)
│ │ │ │ │
* * * * *

Character	Meaning	Example
*	Every value	* * * * * means every minute
,	A list	0 9,17 * * * means 9am and 5pm
-	A range	0 9 * * 1-5 means weekdays
/	A step	*/15 * * * * means every 15 minutes

Common schedules

Expression	Meaning
*/5 * * * *	Every 5 minutes
0 * * * *	Hourly, on the hour
0 0 * * *	Daily at midnight
0 9 * * 1-5	Weekdays at 9am
0 0 1 * *	First of the month
0 0 * * 0	Every Sunday
0 0 1 1 *	Once a year

The day-field trap

This is the single most consequential thing to understand about cron, and it surprises almost everyone.

When both day-of-month and day-of-week are restricted, the expression fires when either matches. Not both.

0 0 1 * 1

Reads naturally as “midnight on the first of the month, if it is a Monday”. It actually means “midnight on the first of the month, and also midnight every Monday”, roughly five times a month rather than once or twice a year.

When only one of the two fields is restricted, only that one applies. The OR behaviour appears only when both are set, which is why it goes unnoticed until a job runs far more often than intended.

Time zones

Cron runs in the system time zone, which on most servers and in most containers is UTC.

timedatectl                    # check the system zone
CRON_TZ=Asia/Jakarta           # set at the top of a crontab

Daylight saving adds two failure modes on systems whose zone observes it:

• A job scheduled in the hour that is skipped in spring may not run at all
• A job scheduled in the hour that repeats in autumn may run twice

The usual mitigation is to schedule anything critical outside the 01:00-03:00 window, or to run the system in UTC and handle local time in the application.

Macros

Most implementations accept these shorthands:

Macro	Equivalent
@yearly	0 0 1 1 *
@monthly	0 0 1 * *
@weekly	0 0 * * 0
@daily	0 0 * * *
@hourly	0 * * * *
@reboot	At startup

Dialects that differ

Six-field cron adds a leading seconds field. Used by Spring, Quartz and some schedulers. A five-field expression pasted into a six-field parser shifts every field by one position, so a daily job becomes an hourly one.

Quartz adds ? for “no specific value”, L for last, W for nearest weekday and # for nth-of-month. These are not standard cron and will error on a Unix crontab.

AWS EventBridge uses six fields and requires ? in one of the two day fields, a rule that exists precisely to sidestep the OR ambiguity described above.

This tool handles standard five-field cron only, and says so rather than guessing.