What it does
The explainer turns an expression into a plain-language sentence in seven languages, lists the next ten run times in any IANA time zone and converts the schedule between standard crontab, Quartz, Spring and AWS EventBridge syntax. The visual builder and presets help when you are starting from scratch.
Every page is available in seven languages, and twenty schedule pages show a common schedule — every five minutes, the first day of the month and many more — side by side in all seven dialects, ready to copy into crontab, a workflow file, a Kubernetes manifest or a Java annotation.
How it works
The parser and scheduler are written in TypeScript and run entirely in your browser. Run times are calculated on wall-clock time with the time-zone data built into your browser, so no external service is involved. Descriptions are generated with the open-source cronstrue library. Each dialect’s rules — field counts, weekday numbering, the question-mark requirement and special characters — are validated separately, so errors point to the exact field.
Who makes it
CronExplain is an independent project, made by the team behind ContrastCheck and the Aspect Ratio Calculator. It is free to use, has no accounts and shows no pop-ups. Suggestions for new dialects or schedules are welcome.
Accuracy and limits
CronExplain models the documented behaviour of each scheduler, not every vendor extension. Jenkins’ H hash syntax, systemd OnCalendar timers and @reboot are not evaluated, and real schedulers may add their own delays. When a schedule matters, confirm the result in the scheduler’s own documentation or a staging environment.
Frequently asked questions
- Is CronExplain free?
- Yes, completely free with no sign-up.
- Which cron dialects are supported?
- Standard crontab, 6-field cron with seconds, Quartz, Spring, AWS EventBridge, GitHub Actions and Kubernetes CronJob.
- How accurate are the next run times?
- They follow each dialect’s documented rules, including daylight-saving transitions. Real schedulers can still start jobs a little late under load.
- Can I link to a specific expression?
- Yes. The URL updates as you type; use “Copy share link” to share it.