About this tool
Cron is the tiny five-part code servers use to run jobs on a timetable: “30 9 * * 1-5” means half past nine on weekdays. It is short, powerful and very easy to get wrong. This tool works both ways. Build a schedule with buttons and it writes the expression for you, or paste an expression you found in a config file and it explains it in a plain sentence, field by field.
Cron is not one language, so the tool speaks four dialects. Unix cron (crontab, Kubernetes, most Linux servers) with its @daily-style shortcuts and optional seconds field; Quartz and Spring, with seconds, a year field and the special L, W and # characters; AWS EventBridge, with its cron( … ) wrapper and fixed UTC clock; and GitHub Actions, which also runs on UTC and never more often than every five minutes. Switch dialect and your schedule is converted, with a note if anything had to change.
The next ten run times are worked out for any time zone, including the days the clocks change. Mistakes get a clear message pointing at the field that is wrong. Everything is calculated in your browser; nothing you type is sent anywhere.
How to use Cron Expression Builder
- Choose your dialect at the top: Unix cron, Quartz / Spring, AWS or GitHub Actions.
- Type or paste an expression into “Cron expression”, or tap one of the common schedules underneath it.
- Read the plain-English sentence. Tap any field box under the expression to edit that part in “Build it”.
- In “Build it”, pick a field tab, then Every, Specific, Range or Every n (and Last / nth in Quartz and AWS). The expression updates as you click.
- Check “Next 10 runs” in your server’s time zone, then press Copy, or copy the ready-made snippet for your crontab, workflow or Spring code.
“0 0 1,15 * 1” looks like “midnight on the 1st and 15th, if it is a Monday”. Unix cron actually runs it on the 1st, the 15th AND every Monday, because when both day fields are set it needs only one to match. The tool spells this out under the sentence.
Features
- Two-way: a visual builder that writes the expression, and a reader that explains any expression you type.
- Four dialects: Unix cron, Quartz / Spring, AWS EventBridge and GitHub Actions, with conversion between them.
- Lists, ranges, steps, month and day names, an optional seconds field and the Quartz year field.
- Quartz and AWS extras: ? for “no specific day”, L for last, W for nearest weekday, # for the nth weekday of the month.
- Shortcuts @yearly, @annually, @monthly, @weekly, @daily, @midnight, @hourly and @reboot in Unix mode.
- Next 10 run times in any time zone, correct across daylight-saving changes, with your own local time alongside.
- Plain-English errors that name the field and the fix, and a warning about the Unix either/or day rule.
- Up to sixteen common schedules in one tap, a syntax cheat sheet, and ready-to-paste snippets for crontab, GitHub, AWS CLI and Spring.
Tips and good to know
- If you mean “and” for two day rules, set only one day field. In Unix cron “0 9 13 * 5” runs on every 13th and every Friday, not just Friday the 13th.
- Day-of-week numbers differ: Unix uses 0–6 with Sunday as 0 (7 also works), while Quartz and AWS use 1–7 with Sunday as 1. Names like MON-FRI avoid the confusion.
- Avoid scheduling jobs between 01:00 and 03:00 in zones with daylight saving. That hour can be skipped or happen twice, and cron versions handle it differently.
- GitHub and AWS always use UTC, so 09:00 in the expression is 09:00 UTC. Use the run list to see what that is in your own time.
Frequently asked questions
Is anything I type sent to a server?
No. Parsing, the plain-English explanation and the run times are all calculated by code running in your browser. Nothing is uploaded or saved, apart from remembering which dialect you last used on this device.
Is it free, and are there limits?
Yes, it is free with no sign-up and no limits. Use it as often as you like.
Does it work on a phone or offline?
Yes. The builder is designed for small screens, and once the page has loaded it keeps working without a connection, because nothing needs the internet.
What does “*/5 * * * *” mean?
Every five minutes: at minutes 0, 5, 10 and so on past every hour, every day. The */5 in the first field is a step of five through all the minutes; the four stars mean every hour, day, month and weekday.
Why is my AWS or Quartz expression rejected without a “?”
Quartz and AWS can’t combine a day of the month with a day of the week, so they make you put ? (no specific value) in one of them. For example, every weekday at 09:30 is “0 30 9 ? * MON-FRI” in Quartz.
Which time zone does cron use?
Unix cron uses the server’s own time zone unless the system sets another one. Quartz uses the Java time zone unless you give one. AWS EventBridge rules and GitHub Actions always use UTC. Pick the matching zone in the run list to see the real times.
What is the difference between 5 and 6 fields?
Standard cron has five fields starting with the minute. Many libraries, including Spring and node-cron, add a seconds field at the front, so a six-field expression usually starts with seconds. AWS also has six fields, but its extra one is the year at the end.
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