Cron every 30 minutes

Yes. Both select :00 and :30 every hour, producing 48 runs daily. The list form states the two clock minutes explicitly; the step form emphasizes the interval. Expression: */30 * * * *

Use 15,45 * * * *. It fires at :15 and :45 instead of at the top and bottom of the hour. Expression: 15,45 * * * *

Use 0,30 9-17 * * 1-5. It fires twice in every included hour, with the final run at 17:30 because 9-17 is inclusive. Expression: 0,30 9-17 * * 1-5

Use */30 0-6 * * * for :00 and :30 from midnight through 06:30. Hour ranges are inclusive. Expression: */30 0-6 * * *

Keep normal runtime below 30 minutes and capacity above one interval's arrivals. Otherwise backlog grows or runs overlap; an hourly cadence halves starts but doubles records per batch.

It is platform-specific. Vixie/cronie can skip or double local :00/:30 matches; GitHub advances nonexistent local times; EventBridge Scheduler skips spring and runs once in the fall overlap. UTC-only Vercel and Cloudflare are unaffected.

Yes. Thirty minutes is above GitHub Actions' five-minute floor and EventBridge's one-minute floor.

Use cron(0/30 * * * ? *). EventBridge requires six fields including year, a ? in one day field, and the cron(...) wrapper. Expression: 0/30 * * * ? *

Use 0 0/30 * * * ?. Quartz puts seconds first, so this fires at second zero of minutes 0 and 30. Expression: 0 0/30 * * * ?

Persist the last completed window boundary and process forward from it. Standard cron does not replay a missed :00 or :30 start, so deriving work only from the current clock can skip a window.

This cadence makes 48 calls per day, so include API quotas, execution cost, and retries in capacity planning. Crontap can run it with retries for failed HTTP calls.

*/30 * * * *. Paste this into Linux crontab, Vercel cron, node-cron, robfig/cron, or a Kubernetes CronJob to run a job every 30 minutes; AWS EventBridge and Quartz need the six-field form.

The editor above shows the next 30+ runs on a calendar in your local timezone, plus a plain-English description. If the calendar matches your intent, the cron is correct.

Linux crontab, Vercel cron jobs, node-cron, robfig/cron, and Kubernetes CronJob accept the five-field form as is. AWS EventBridge and Quartz use six-field expressions with a ? in one of the day fields; see the AWS and Quartz guides for the conversion. Vercel's free Hobby plan caps the minimum frequency at once-per-day; the Pro plan removes that cap.

Most schedulers will start the new run anyway, leading to overlap. To prevent this, wrap the command with flock -n /tmp/myjob.lock /path/to/script.sh on Linux, or set concurrencyPolicy: Forbid on Kubernetes CronJob. Vercel and EventBridge may overlap runs if the previous one is still executing; make the handler idempotent.