cron expression · plain english
Cron at 3 AM nightly
Fires at 03:00 every day — quietest hour on most servers (after midnight cron stampede, before morning traffic). Standard for heavy nightly batch jobs.
beginner
POSIX / Jenkins / Quartz / AWS
0 3 * * *
cron at 3 am nightly.
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 3 * * * | minute=0, hour=3 |
| Jenkins | H 3 * * * | minute hash; hour fixed |
| Quartz (Java) | 0 0 3 * * ? | 6-field |
| systemd timer | OnCalendar=03:00 | fires at 03:00:00 |
| AWS EventBridge | cron(0 3 * * ? *) | 3 AM UTC by default |
Common pitfalls
- DST handover: spring-forward eats the 02:00→03:00 hour. The 03:00 fire still happens (local clock just jumped to 03:00). Fall-back: 02:00 happens twice but 03:00 fires once. Cadence preserved.
- Containers in UTC mode + 03:00 schedule = 22:00 EST or 04:00 CET. Verify host TZ before assuming '3 AM local'.
- Heavy batch jobs at 03:00 across 100+ servers in same DC = network/storage spike. Stagger with H or random offsets.
Use cases
- Nightly database backup
- Log compaction
- Stale cache eviction
- Index rebuild
- Snapshot retention purge
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) · cron: every 15 minutes · cron: every day at noon (12:00)