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cron-expression

A cron expression is a 5-field string that defines a recurring schedule for unix cron, Kubernetes CronJobs, GitHub Actions, AWS EventBridge, or any other cron-compatible scheduler. The ZTools Cron Expression tool generates expressions from a visual builder (minute, hour, day-of-month, month, day-of-week pickers), parses existing expressions to plain-English ("Every weekday at 9:00 AM"), and previews the next 10 firing times in your local timezone. Supports standard 5-field syntax (Linux cron, Kubernetes), 6-field syntax with seconds (Quartz, Spring), and special predefined strings (@daily, @hourly, @reboot).

Use cases​

Scheduling a Kubernetes CronJob​

Need a job that runs every Sunday at 03:00 UTC? Use the visual builder to pick the schedule, copy the resulting 0 3 * * 0, and paste it into your CronJob schedule: field. The preview confirms the next run times match your intent before you deploy.

Setting up a GitHub Actions scheduled workflow​

GitHub Actions uses standard 5-field cron in schedule.cron. Build your expression, verify the next 10 run times, and paste into the workflow file — no risk of typo-induced silent misfires.

Decoding an inherited cron expression​

You inherit a server with */15 9-17 * * 1-5 in crontab. Paste it into the decoder; the tool renders "Every 15 minutes, between 09:00 and 17:00, Monday through Friday" — instant comprehension without manual field decomposition.

Validating an AWS EventBridge schedule​

AWS EventBridge uses a 6-field cron with optional year. Switch the tool to 6-field mode, build the expression, and use the preview to ensure your daily backup actually fires at midnight UTC and not noon.

How it works​

  1. Choose the cron flavor — Standard 5-field (Linux, Kubernetes, GitHub Actions) or 6-field (Quartz, AWS EventBridge with seconds).
  2. Use the visual builder OR paste an existing expression — Builder: dropdowns for minute, hour, day, month, day-of-week. Decoder: paste any valid cron string.
  3. See the plain-English description update live — Every change to the expression updates the description: "At 09:00 AM, Monday through Friday".
  4. Preview the next 10 firing times — The tool computes upcoming run times in your local timezone (auto-detected) and your chosen timezone. Spot edge cases like missed midnight crossings or DST shifts.
  5. Copy the expression — One-click copy. Paste into your scheduler's configuration and deploy with confidence.

Examples​

Input: Build: every weekday at 9:00 AM

Output: 0 9 * * 1-5

Input: Decode: */15 9-17 * * 1-5

Output: Every 15 minutes, between 09:00 and 17:00, Monday through Friday

Frequently asked questions​

What is the difference between 5-field and 6-field cron?

5-field is the classic Linux/POSIX format: minute, hour, day-of-month, month, day-of-week. 6-field prepends a seconds field (Quartz, Spring, AWS EventBridge). Some flavors append a year field for a 7th field.

How do I run a job every 15 minutes?

Use */15 * * * *. The */N syntax means "every N units" of that field. Equivalent to 0,15,30,45 * * * *.

What does "@daily" mean?

Shorthand for "0 0 * * *" — runs once per day at midnight. Other shorthands: @hourly, @weekly, @monthly, @yearly, @reboot.

Why might my cron job not run when I expect?

Common causes: the cron daemon timezone differs from your assumed timezone (set CRON_TZ or use UTC); the user's shell environment is not loaded (use full paths); the expression has a typo. Use this tool's preview to verify.

How do I run a job only on the last day of the month?

Standard cron does not support "last day". Use 0 0 28-31 * * combined with a guard [ "$(date +\\%d -d tomorrow)" = "01" ] in the script. Quartz supports L for last day natively.

What's the difference between day-of-month and day-of-week?

Day-of-month is 1-31; day-of-week is 0-6 (Sunday=0) or 1-7 depending on flavor. When both are specified, classic cron treats them as OR (either condition fires the job).

Tips​

  • Always preview the next 10 firing times — catches typos before they cost you a missed nightly job.
  • Use UTC in production to avoid DST surprises; document the timezone in a comment alongside the cron line.
  • Avoid scheduling many jobs at exactly minute 0 — spread the load across the hour to reduce thundering-herd CPU spikes.
  • For complex schedules (every 2nd Tuesday of the month), use a real scheduler like Airflow or Temporal — cron is for simple cases.

Try it now​

The full cron-expression runs in your browser at https://ztools.zaions.com/cron-expression — no signup, no upload, no data leaves your device.

Open the tool ↗

Last updated: 2026-05-05 · Author: Ahsan Mahmood · Edit this page on GitHub