Cron Expression Builder (5-Field Unix)

Scheduling · cron · devops

Build classic five-field Unix cron expressions visually instead of guessing asterisks. Choose minute, hour, day, month, and weekday values, copy the expression, then verify next run times with the companion parser.

5-field Unix cron Visual field builder Human-readable hint Copy-ready expression Client-side only

Why cron is easy to get wrong

Cron schedules background jobs on servers, in Kubernetes CronJobs, CI schedules, and cloud schedulers. A single off-by-one in the day-of-week field or mixing “every day at 9” with the wrong timezone can mean missed backups or noisy pages at 2 a.m. A builder reduces syntax mistakes; you still own timezone and platform semantics.

Field reference (classic 5-field)

Field	Values	Examples
Minute	0–59	`0`, `*/15`, `0,30`
Hour	0–23	`9`, `0-6`, `*/2`
Day of month	1–31	`*`, `1`, `1-7`
Month	1–12	`*`, `1,7`
Day of week	0–7 (often 0 and 7 = Sunday)	`1-5` weekdays

Common forms: * (any), A-B (range), A,B (list), */N (step). Some platforms add a seconds field (6-field) or year — always confirm your runner.

How to use this builder

Adjust each field (or start from a sensible default) until the human-readable hint matches your intent.
Copy the generated expression into crontab, a Helm chart, or your scheduler UI.
Open the Cron Parser to preview upcoming run times and catch “never fires” mistakes.
Document the timezone next to the expression (UTC vs local is a frequent production bug).

Useful example schedules

Goal	Expression
Every day at 09:00	`0 9 * * *`
Every 15 minutes	`/15 * * *`
Weekdays at 18:30	`30 18 * * 1-5`
First of month at midnight	`0 0 1 * *`
Every Sunday at 03:00	`0 3 * * 0`

Day-of-month + day-of-week: When both are restricted (not *), many cron daemons treat the schedule as “either field matches” (OR), not AND. That surprises people. Prefer leaving one of them as * unless you know your platform’s rules.

Platform differences to watch

AWS EventBridge, GCP Cloud Scheduler, GitHub Actions — may use cron-like syntax with their own limits and timezones.
Quartz / Spring — often 6 or 7 fields including seconds.
systemd timers — different language entirely; don’t paste crontab blindly.
DST — “every day at 2:30 local” can skip or double on transition days; prefer UTC for critical jobs.

FAQ

Is this 5-field or 6-field cron?

This builder targets classic five-field Unix cron (minute through day-of-week). If your system requires seconds, add that field according to its docs.

Does the builder run jobs?

No. It only constructs the expression. Scheduling is done by your OS, orchestrator, or cloud service.

Is anything sent to a server?

No — field assembly is local. Privacy Policy.

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