Support: Cron Expression Explainer

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Common questions

What do the five fields mean?

In order: minute (0-59), hour (0-23), day of month (1-31), month (1-12 or JAN-DEC) and day of week (0-7 or SUN-SAT, where 0 and 7 are both Sunday). A star means every value.

What does */15 mean?

Every 15th value from the start of the field: in the minute field, minutes 0, 15, 30 and 45. 9-17/2 means every second value from 9 through 17.

Why does my job run on more days than I expected?

When both the day of month and the day of week are restricted, cron runs when either matches. 0 0 1 * 1 runs on the first of each month and also every Monday.

Which time zone does cron use?

The clock of the machine running it. Servers, containers and GitHub Actions usually run on UTC, so switch the next runs to UTC to match.

Can it read a seconds field?

Yes. A line with six fields is read with seconds first, as Spring, Quartz-style and several job libraries use. Five fields are the classic crontab format.

What are @daily and @reboot?

Shortcuts: @hourly, @daily (or @midnight), @weekly, @monthly and @yearly (or @annually) stand for their five-field forms. @reboot runs once when the cron service starts.

Why does it say the job never runs?

The day and month never meet, as with the 30th of February or the 31st in a 30-day month. Cron accepts such lines but never fires them.

Is it free?

Yes, completely free, with no sign-up.