Cron field reference
| Field | Range | Special |
|---|---|---|
| Minute | 0–59 | * , - / |
| Hour | 0–23 | * , - / |
| Day of month | 1–31 | * , - / |
| Month | 1–12 | * , - / |
| Day of week | 0–6 (Sun=0) | * , - / |
Syntax cheatsheet
*— every value in the range5— exact value1-5— range (inclusive)1,3,5— list*/5— every 5 starting from 00-30/10— every 10 from 0 to 30
The day-of-month / day-of-week gotcha
When both day-of-month and day-of-week are restricted (not *), POSIX cron matches if
either is satisfied — they're OR'd, not AND'd. So 0 0 15 * 1 means "midnight on the
15th of every month OR every Monday," which is probably not what you intended.
This tool uses the POSIX OR rule (consistent with cron, Jenkins, etc).
Cron pitfalls
- Timezone — classic Linux cron runs in the server's local timezone. DST transitions can make a job run twice or skip a run. For safety, set the machine to UTC or use a scheduler that supports explicit timezones (systemd timers, Quartz).
- Missed runs — if the machine is off at the scheduled time, the run is gone. Use
anacronor a job runner with catch-up semantics. - Overlap — if your job takes longer than the interval, you'll end up with concurrent runs. Wrap in a lock file or use a scheduler that prevents overlap.
- Seconds — standard cron doesn't have a seconds field. If you see a 6-field cron, it's a non-standard extension (Quartz, some JS libraries). This tool is 5-field POSIX.
FAQ
Does this support 6-field (with seconds) expressions?
No — 5-field POSIX only. If you see 0 0 12 * * ?, that's Quartz — drop the first field for standard cron.
Does it support @daily / @hourly?
Not yet. Use the preset dropdown for equivalents.
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Pillar
Part of Dev Productivity — regex, cron, timestamps, HTTP, color, word counter, aspect ratio, case.
Written by Mian Ali Khalid. Last updated 2026-04-25.