Cron Expression Explainer
Translate cryptic cron schedules into plain English with validation and weekly frequency.
Decode cron expressions into plain English instantly. Free cron explainer with field validation, step/range support and next-run hints.
Calculator Inputs
About Explain Cron
Translate cryptic cron schedules into plain English with validation and weekly frequency.
Paste any 5-field cron expression. Each field is validated (ranges, steps, lists, and the Sunday 0/7 alias), then rendered as sentences: the times it fires, the months it covers, and the day logic — including cron’s notorious AND between day-of-month and weekday.
The weekly run count exposes surprises like */5 minutes meaning ~2,000 runs a week. Quartz-style 6-field expressions are out of scope. Everything runs in your browser.
Where it is used
Reviewing inherited crontabs, verifying deploy windows, teaching cron syntax, and catching day-of-month vs weekday mistakes.
How to use the Explain Cron
- Cron Expression (5 fields) — enter the value (e.g. */15 9-17 * * 1-5).
- Calculate — press the Calculate button to see the result instantly above.
Formula
Validate each field (lists/ranges/steps) → describe time, month, and day constraints.
Examples
Example
Frequently Asked Questions
- Why did my job run on an unexpected day?
- Almost always the day-of-month/weekday AND quirk: when both are restricted, cron fires when EITHER matches, not both. Restrict only one side.
- Does 7 mean Sunday?
- Yes — 0 and 7 both mean Sunday in day-of-week. This tool normalizes 7 to Sunday automatically.
- How do I run something every 90 minutes?
- You cannot express that in one line — cron has no cross-hour steps. Use two lines (e.g. 0 9,12,15… and 30 10,13,16…) or a sleep-based wrapper.