About Cron Expression Builder
Cron Expression Builder turns the five (or six) cryptic fields of a cron schedule into something you can read and edit visually. Pick days, months, hours and minutes from dropdowns and the expression updates live; or paste an existing schedule and see it explained in plain English plus the next few times it will fire. Validates against both standard Unix cron and the extended Quartz/AWS variants. Handy for setting up cron jobs, GitHub Actions schedules, Kubernetes CronJobs, and AWS EventBridge rules without second-guessing the syntax.
- No uploads
- Browser-only
- Works offline
- 100% free
How it works
- 1
Build with the visual editor
Select minute, hour, day-of-month, month, and day-of-week ranges from grid pickers. The expression in the output box updates as you click.
- 2
Or paste an expression
Drop in something like '0 9 * * 1-5' and the builder reverse-engineers the picker, shows a sentence description ('At 09:00 on weekdays'), and validates each field.
- 3
Preview the next runs
A list of the next 5–10 trigger times is calculated against your local timezone, so you can sanity-check that 'every other Tuesday at 3am' really means what you think.
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Frequently asked questions
Are my files uploaded to a server?
No. Every tool on SnapToolz runs entirely inside your browser using JavaScript and WebAssembly. Your file is read locally, processed in memory, and the result is offered as a download. Nothing is sent to a server — there isn't one to send to.
Does it support Quartz / AWS / Spring cron extensions?
Yes — toggle six-field mode for a seconds column (Spring, Quartz, AWS EventBridge), and special tokens like @yearly, @hourly, L (last day of month), W (nearest weekday) and # (nth weekday) are recognised. Standard Unix five-field cron is the default since it covers the most common use cases — crontab, Kubernetes CronJob, GitHub Actions.
Why does the next-run preview not match my server?
Cron schedules run in whichever timezone the host is configured for. The preview uses your browser's local timezone for readability — if your server runs in UTC, set your machine to UTC temporarily or mentally apply the offset. GitHub Actions, for example, always fires in UTC.
Will it warn me about a schedule that never fires?
Yes — combinations like 'Feb 31' or 'day-of-month=30 AND day-of-week=Sun (every year forever)' are flagged. The validator also points out commonly mistaken patterns, like using '* * * * *' (every minute) when you meant '0 * * * *' (top of every hour).
Does it work offline?
Yes. SnapToolz is a Progressive Web App. After your first visit, the app is cached on your device and every tool keeps working without an internet connection.
Is SnapToolz free?
Yes — every tool is 100% free with no sign-up, no watermark, no hidden tier. The whole platform is open source and we have no plan to gate features.