Question 1

What is a cron expression?

Accepted Answer

A cron expression is a string of five fields separated by spaces that defines a schedule. It is used by Unix-like operating systems (via crontab) and many scheduling tools to run tasks at specific times or intervals.

Question 2

What do the five fields mean?

Accepted Answer

The five fields are, from left to right: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). An asterisk (*) in any field means "every" value.

Question 3

What does the slash (/) mean in a cron expression?

Accepted Answer

The slash defines a step value. For example, */15 in the minute field means "every 15 minutes" (0, 15, 30, 45). You can also combine it with a starting value, like 5/15, which means "every 15 minutes starting at minute 5" (5, 20, 35, 50).

Question 4

How does cron handle day-of-month and day-of-week together?

Accepted Answer

When both day-of-month and day-of-week are set to non-wildcard values, the POSIX standard uses OR logic — the job runs if either condition is met. For example, "0 9 15 * 1" runs at 9:00 AM on the 15th of every month AND every Monday.

Question 5

Does this tool support seconds or year fields?

Accepted Answer

No. This tool uses the standard 5-field cron format (minute, hour, day-of-month, month, day-of-week). Some systems like Quartz or Spring support 6 or 7 fields with seconds and year, but those are non-standard extensions.

Cron Expression Builder

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