tooloora

Cron every 15 minutes — */15 * * * * explained

The quarter-hour rhythm: four runs per hour at :00, :15, :30 and :45, and why so much traffic piles up right there.

Runs locally — nothing is uploaded

Examples

In plain words

Every 15 minutes, every day.

Field by field

  • */15Minute

    every 15 minutes

    Matches: 0, 15, 30, 45

  • *Hour

    every hour

    Matches: 0, 1, 2, 3, 4, 5 … 23

  • *Day of month

    on every day of the month

    Matches: 1, 2, 3, 4, 5, 6 … 31

  • *Month

    in every month

    Matches: Jan, Feb, Mar, Apr, May, Jun … Dec

  • *Day of week

    on every weekday

    Matches: Sun, Mon, Tue, Wed, Thu, Fri, Sat

Next runs

Calculating the next runs …

These times apply in the time zone configured on the server. Cron converts nothing; this preview uses your device clock.

The expression stays in your browser — it is never sent to a server.

Other expressions

* * * * *every minute*/5 * * * *every 5 minutes*/30 * * * *every 30 minutes0 * * * *every hour0 0 * * *daily at midnight0 3 * * *daily at 3 a.m.0 9 * * 1-5weekdays at 9 a.m.0 0 * * 0every Sunday0 0 1 * *on the 1st of each month

*/15 * * * * runs the job four times an hour: at minute 0, 15, 30 and 45, in every hour of every day, which comes to 96 runs a day. Fifteen divides 60 evenly, so the gap stays the same across the hour boundary — a property not every step width has.

What is a quarter-hour schedule good for?

It is the usual compromise between freshness and load: synchronising mailboxes, refreshing a cache, pulling exchange rates, collecting metrics. Data is at most fifteen minutes old, and a job that occasionally takes two or three minutes still has plenty of room before the next start. Monitoring dashboards with a fifteen-minute grid line up neatly with it.

Why does the server get busy at :00, :15, :30 and :45?

Because everyone picks the same round minutes. On a machine with a dozen cron entries, half of them fire at minute 0, and backups, log rotation and monitoring agents join in. Spreading the load costs one character: 3-59/15 keeps the quarter-hour rhythm but runs at 3, 18, 33 and 48 instead.

How do I restrict it to working hours?

Narrow the hour and weekday fields: */15 8-18 * * 1-5 runs every quarter of an hour between 8 a.m. and 6:59 p.m., Monday through Friday. Note the hour range is inclusive on both ends, so 8-18 covers the whole 18th hour up to 18:45 — a frequent off-by-one when people expect it to stop at six.

How to add the expression

  1. Decide whether the job may run at night; if not, add an hour range such as 8-18.
  2. Add the line */15 * * * * plus your command to the crontab and save it.
  3. If the machine already has several jobs, shift yours with 3-59/15 so they do not all start together.
  4. Compare the next run times shown above with what your monitoring expects.

Frequently asked questions

Is */15 the same as 0,15,30,45?

Yes, both notations produce exactly the same four minutes. The list form is handy if you later want an irregular pattern such as 0,20,50; for a regular rhythm the step form is shorter and less error-prone.

What happens during the daylight saving switch?

A quarter-hour job is barely affected: in spring one hour is skipped, so four runs are missed, and in autumn the repeated hour gives four extra runs. Jobs that must run exactly once should not rely on a fine-grained interval.

Can I run it every 15 minutes but only on weekends?

Yes: */15 * * * 6,0 covers Saturday and Sunday. Remember that cron numbers Sunday as 0 and also accepts 7 for it, so 6,7 and 6,0 mean the same thing.

Do you store the expressions people type in?

No. There is no server involved in the explanation at all: the parser, the description and the next run times run inside your browser tab, and nothing about your schedule is logged or saved.