Field breakdown
*/15 expands the minute field to 0, 15, 30 and 45. Because fifteen divides evenly into
sixty, runs land on the quarter hour in every hour without drifting, which makes logs unusually easy to
read: any timestamp ending in :00, :15, :30 or :45 is this job.
*/15, 0,15,30,45 and 0-45/15 are three spellings of the same
schedule. The first is idiomatic; the second is the most portable.
Typical uses
- Pulling a feed or an external API where a quarter hour of staleness is acceptable.
- Rebuilding a materialised view or search index.
- Retrying a queue of failed deliveries.
- Certificate and token renewal checks, where the work is a cheap no-op almost every time.
Using it
# crontab
*/15 * * * * /usr/local/bin/refresh-index --quiet# GitHub Actions
on:
schedule:
- cron: "*/15 * * * *"Fifteen minutes is the shortest interval GitHub documents as reasonable for scheduled workflows, and even then runs can be delayed under load. For anything time-critical, trigger from your own scheduler instead.
Restricting it to working hours
*/15 9-17 * * 1-5 is the most common refinement: quarter-hourly between 09:00 and 17:59, Monday through Friday. That is 36 runs per working day and 180 a week, down from 672.
The hour range 9-17 covers all of hour 17, so the final run is 17:45. If you need the
day to end at 17:00 exactly, use 9-16 plus a separate 0 17 * * 1-5 line.
Adding a day-of-month restriction on top of the weekday one would invoke cron's day-of-month/day-of-week OR rule rather than combining the two conditions — worth reading before you restrict both fields at once.
Variations
| Expression | Runs |
|---|---|
| */15 * * * * | Every 15 minutes, 96 times a day. |
| 0,15,30,45 * * * * | Identical, written as an explicit list. |
| */15 9-17 * * 1-5 | Quarter-hourly during office hours on weekdays. |
| */15 * * * 6,0 | Quarter-hourly at weekends only. |
| 7-52/15 * * * * | Quarter-hourly, offset to :07, :22, :37 and :52. |