Cron: every 30 minutes

Two runs an hour, on the hour and at half past. */30, 0,30 and 0-59/30 are three ways of writing the same schedule.

Open in Cron Parser The expression is filled in: change it and watch the next runs.

Expression

*/30 * * * *

Meaning

At every 30th minute: :00 and :30

Your time zone

Platform	Written as	Note
Linux crontab	/30 * * *	Five fields, in the server's local time zone. A `%` in the command has to be escaped as `\%`.
GitHub Actions	- cron: '/30 * * *'	Five fields, in UTC unless a `timezone` (an IANA name such as `Europe/Warsaw`) is set next to `cron`. Default branch only. The shortest interval is 5 minutes; when GitHub is busy, runs start late and some are dropped.
Kubernetes CronJob	schedule: "/30 * * *"	Five fields, in the controller's time zone unless `spec.timeZone` is set (Kubernetes 1.27 and later). `concurrencyPolicy` decides what happens when runs overlap.
systemd timer	OnCalendar=*:0/30	Its own calendar syntax, in a `.timer` unit, local time. `hourly`, `daily` and `monthly` match cron, but `weekly` means Monday. `Persistent=true` catches up on runs missed while the machine was off.
AWS EventBridge	cron(0/30 * * * ? *)	Or `rate(30 minutes)`, which counts from when the rule was created.
Quartz / Spring	0 0/30 * * * ?	Six fields, seconds first. Quartz needs `?` in one of the day fields and counts Sunday as 1; Spring accepts `?` and numbers days like cron.

30 * * * * runs once an hour

Without the slash, the job runs only at half past each hour.
Every 30 seconds in Quartz

Quartz starts with a seconds field, so 0/30 * * * * ? copied from a Quartz example means every 30 seconds, not every 30 minutes.
Two runs at other minutes

A list sets them freely: 10,40 * * * * runs at :10 and :40.