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May 11, 2026·data

Cron Builder

Write a cron expression, get a human-readable description + next 5 runs + interactive field builder. Sanity-check yourself when wiring QStash / GitHub Actions / Kubernetes CronJobs.

cron · scheduling · qstash

PreviousArgon2id Parameter ConfigurerNextHMAC Lab

Is 0 9 * * 1-5 "Mon-Fri at 09:00 UTC" or "9 minutes past every hour"? Cron syntax is confusing. This lab parses the expression, lists the next 5 runs in your timezone, and explains each field.

CronBuilder — 5-field POSIX cron

at minute 0, hour 9, on Mon–Fri

min
hour
day
month
dow
next 8 runs (UTC)
  1. #12026-05-14 09:00 UTCin 13h 45m
  2. #22026-05-15 09:00 UTCin 1d
  3. #32026-05-18 09:00 UTCin 4d
  4. #42026-05-19 09:00 UTCin 5d
  5. #52026-05-20 09:00 UTCin 6d
  6. #62026-05-21 09:00 UTCin 7d
  7. #72026-05-22 09:00 UTCin 8d
  8. #82026-05-25 09:00 UTCin 11d
min
0–59hour
0–23dom
1–31month
1–12dow
0=Sun

Field reference

Cron expression fields
0 9 * * 1-5
minute
0–59
hour
0–23
day-of-month
1–31
month
1–12, JAN–DEC
day-of-week
0–6, SUN–SAT

Common patterns

ExpressionMeaning
* * * * *every minute
*/5 * * * *every 5 minutes
0 * * * *top of every hour
0 9 * * *daily at 09:00
0 9 * * 1-5weekdays at 09:00
0 0 1 * *midnight on the 1st of every month
30 4 * * 0Sunday 04:30 (weekly cleanup)

Pitfalls

  • Day-of-month AND day-of-week together → most cron implementations use OR logic (each condition fires independently). Vixie cron, GNU mcron, QStash all do this. AWS EventBridge uses 6-field cron with different semantics.
  • @reboot, @daily, @hourly macros exist in some implementations, not universal
  • Seconds field (6th) exists in AWS, Kubernetes, Quartz; not in standard cron