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yutils
Cron Expression Builder
Example

Input (cron expression)

0 9 * * 1-5

Output

Human: At 09:00 AM, Monday through Friday
Next runs:
  - 2026-05-14 09:00 (Thu)
  - 2026-05-15 09:00 (Fri)
  - 2026-05-18 09:00 (Mon)
  - 2026-05-19 09:00 (Tue)
  - 2026-05-20 09:00 (Wed)

Note

5 fields: minute, hour, day, month, weekday. Human-readable description via cronstrue plus the next 5 firing times via cron-parser. Invalid expressions error out immediately.

Usage / FAQ

When to use

  • Validate Kubernetes CronJob or GitHub Actions schedules
  • Write expressions for AWS EventBridge or Cloud Scheduler
  • Decode complex cron strings like `*/15 9-17 * * MON-FRI`
  • Preview the next firing times to confirm intent
  • Learn the five-field layout (minute hour day month weekday)

FAQ

Q.5 fields vs 6 fields (seconds)?
A.Standard cron has 5 fields. Quartz / Spring Schedule add a leading seconds field for 6. This tool uses the 5-field standard.
Q.What's the difference between `0` and `*`?
A.`0 * * * *` fires at minute 0 of every hour (`:00`). `* 0 * * *` fires every minute from 0:00 to 0:59. `*` means "any", a number means "only this value".
Q.How are timezones handled?
A.Cron itself has no timezone — it follows the runtime's TZ. This tool uses the browser's local TZ for next-firing previews. A UTC container will fire 9 hours offset from KST.
Fun facts

  • The name *cron* comes from Greek χρόνος (chronos). It first shipped in Unix V7 (1975), but the 5-field syntax (minute/hour/day/month/day-of-week) we use today was standardized by Paul Vixie's *vixie cron* in 1987 — the basis for nearly every modern Linux distro.

    Wikipedia — cron

  • Early cron woke every minute to re-read crontab. Vixie cron reloads only when crontab is modified and otherwise sleeps — that's why everyone thinks of cron as 'minute-granularity'.

    man cron(8)

  • Whether day-of-week 0 means Sunday or Monday varies by cron flavor. Vixie/cronie accept both 0 and 7 as Sunday. POSIX says 0=Sunday but some implementations use ISO 8601 (0=Monday). Use names like `SUN` or write `0,7` to be safe.

    POSIX crontab

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