Cron Expression Explainer
Turn a cron expression into plain English and see its next run times in your browser.
- Runs in your browser, files never leave your device
- Free, open source, no account, no ads
- Works offline after the first visit
Explain a cron expression
How it works
- Type or build an expression. Paste a cron line, tap a preset, or open the builder and pick minutes, hours, days and months from menus. Switch mode for seconds or Quartz syntax.
- Read what it means. A plain-English sentence and a field-by-field breakdown update as you type. Mistakes are shown in red on the exact field.
- Check when it runs. Pick the server's time zone and see the next 10 to 50 run times, daylight saving included. Copy the result or download it as CSV or a calendar file.
Questions, answered
Is my cron expression sent anywhere?
No. Cron Expression Explainer runs entirely in your browser. Parsing, the description and the run times are all computed with JavaScript on your device, and nothing you type is sent to a server. You can disconnect from the internet and it keeps working.
What is the difference between standard, seconds and Quartz mode?
Standard cron (Linux cron jobs, GitHub Actions, Kubernetes CronJobs) has five fields: minute, hour, day of month, month and day of week. Some schedulers such as Spring add a seconds field at the front, which gives six. Quartz also starts with seconds, allows an optional year at the end, numbers weekdays 1 (Sunday) to 7, and adds ?, L (last), W (nearest weekday) and # (for example 6#3, the third Friday).
Why does my job run on more days than I expected?
In classic cron, if both the day of month and the day of week are restricted, a day that matches either one runs. So 0 0 1 * MON runs on the 1st of each month and also every Monday. The description says "or" when that rule applies. Quartz avoids this by requiring ? in one of the two fields.
How are time zones and daylight saving handled?
Run times are computed in the time zone you choose, using your browser's own time zone data. When clocks spring forward, a time that does not exist that day (such as 02:30) is skipped. When clocks fall back, a repeated time runs once. Some cron daemons behave differently around these hours, so check yours if a job falls inside one.
Is it really free, and does it work offline?
Yes to both. It is open source under the MIT license, with no account, no limits and no ads. After your first visit the page is cached by a service worker, so it loads without a connection, and you can install it from your browser's menu as an app.
Was this written by AI?
Yes. Cron Expression Explainer was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you rely on it for a production schedule.
Built by one person, given away for free
Cron Expression Explainer is a free alternative to paid tools like [removed].guru and cron expression generators. If it earns a place in your bookmarks, a coffee keeps the updates coming.
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