Cron Expression Descriptor
Cron time format
Cron syntax is used by Unix operating system to schedule the jobs at different moments in time. Starting from this many other systems use this simple notation for scheduling tasks. For example, Azure functions use the Ncrontab library for time triggers.
This online tool will give you a clear understanding of your cron job expression. You can also see the next 100 occurrences in order to see when your tasks will be executed.
The difference between cron and ncrontab syntax is that the last one uses also the sixth field for seconds.
Cron syntax
The CRON format looks like this SECONDS MINUTES HOURS DAYS MONTHS DAYS-OF-WEEK.
| Field | Range |
| Seconds | 0-59 |
| Minute | 0-59 |
| Hour | 0-23 |
| Days | 1-31 |
| Months | 1-12 or you can specify the short name of the month: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec |
| Day of the week | 0-7 -> 0 and 7 is for Sunday. You can also specify the first 3 letters of the name of the day: Mon, Tue, Wed, Thu, Fri, Sat, Sun. |
A single wildcard * means all values from that range. For example, if you set the wildcard * for the hour field, it will run every hour. You specify a single value if you only want to run once or you can specify multiple values separated by comma in case you need to run multiple times.
Cron syntax also allows you to specify a range of values (0 7 * * MON-FRI this expression will execute at 7 AM, Monday through Friday).
You can also specify every x element of a range by using a slash. */3 this means every third element of that field.
Using a question mark in the Day of the week field or Day field, you mention that you don't need a specific value.
A field can accept all types of notation (e.g. 1-3,5,*/8).
Cron every 5 minutes
For example, the cron syntax that you need to run your job every 5 minutes is */5 * * * *
The expression descriptor uses the NCrontab library to convert the CRON time into a human-readable form.