cron expression · plain english
Cron twice a day
Fires at 00:00 and 12:00 every day — 12 hours apart. Used for jobs that need biannual heartbeat without the cost of hourly polling.
beginner
POSIX / Jenkins / Quartz / AWS
0 0,12 * * *
cron twice a day.
Next 5 fire times
Computed live in your local timezone. The cron expression itself is timezone-agnostic — these times reflect your browser clock.
Cross-system syntax variants
Same intent, different schedulers. Use this table when migrating between systems.
| System | Expression | Note |
|---|---|---|
| Standard cron (POSIX) | 0 0,12 * * * | explicit hour list |
| Cron (alt step) | 0 */12 * * * | equivalent — step of 12 starting from 0 |
| Jenkins | H H/12 * * * | H/12 produces twice-daily on stable offset |
| Quartz (Java) | 0 0 0,12 * * ? | 6-field, explicit hours |
| AWS EventBridge | cron(0 0,12 * * ? *) | explicit hour list — clearer than rate(12 hours) |
Common pitfalls
- rate(12 hours) is NOT identical to twice-daily — it depends on creation time. Use cron() for wallclock-aligned schedules.
- Midnight is the noisiest cron slot. If your twice-daily can shift, push to 01:00/13:00 to avoid load spikes.
- User-facing jobs at 00:00 reach Asia-Pacific users mid-morning, Americas mid-evening. Adjust per audience.
Use cases
- Daily/morning + nightly batch pair
- Sync of bidirectional data systems
- AM/PM digest blast
- Server-side cache rebuild for heavy queries
Translate any cron expression
cronwtf takes any cron string and returns plain-English description plus the next 5 fire times in your timezone. Standard 5-field, Jenkins H, Quartz 6-field — all supported.
Open cronwtf
Related cron schedules
cron every friday at 5 pm (end of work week) · cron on the last day of every month (quartz only) · how to run a cron job every 10 minutes · how to run cron daily at midnight