Cron: Every 30 Minutes
*/30 * * * * fires twice an hour, at :00 and :30. It's a common choice when a job needs to run more than hourly but doesn't need quarter-hour or finer precision — think periodic backups, moderate-traffic cache refreshes, or non-urgent notification digests.
*/30 * * * *
Examples & Variations
Common Mistakes
- Writing 0,30 * * * * and */30 * * * * as if they might behave differently — they're exactly equivalent, just different notations for the same schedule.
- Using half-hourly cron for something that genuinely needs to react within minutes — this interval is too coarse for anything latency-sensitive.
- Forgetting that a half-hour window is often plenty of time for a slow job to still be running when the next invocation starts — overlap protection still matters.
Best Practices
- This interval is a solid default for periodic backups of small-to-medium datasets where minute-level freshness isn't required.
- If multiple jobs run every 30 minutes, stagger their minute offsets (0,30 vs 15,45) so they don't all compete for the same resources simultaneously.
- Document why the 30-minute interval was chosen in your crontab or job config — it saves the next engineer from guessing whether it's arbitrary or load-bearing.
Frequently Asked Questions
- What's the difference between */30 and 0,30 in the minute field?
- None — */30 is shorthand notation that expands to exactly 0,30. Both produce a job that runs at the top and bottom of every hour.
- Can I offset a 30-minute schedule to run at :15 and :45 instead?
- Yes — use an explicit list: 15,45 * * * *. Step syntax (*/30) always starts from 0, so an offset requires listing the exact minutes.
- Is 30 minutes too infrequent for uptime monitoring?
- For most services, yes — dedicated uptime monitors typically check every 1–5 minutes so an outage is caught quickly. Reserve 30-minute cron for less time-sensitive maintenance tasks.
Related Tools
Cron Parser
Translate cron expressions to plain English
Cron Cheat Sheet
Quick reference for cron syntax, special characters, and shortcuts
Cron Examples Library
Browse and search common cron expression examples
Cron: Every 15 Minutes
The cron expression for every 15 minutes is */15 * * * *. See quarter-hour scheduling examples, mistakes to avoid, and best practices.
Cron: Every Hour
The cron expression for every hour is 0 * * * *. See hourly scheduling examples, common mistakes, and best practices for cron jobs.
Cron: Every Day
The cron expression for every day is 0 0 * * *, running once daily at midnight. See daily scheduling examples and best practices.