Cron Explainer

Standard crontab (Vixie/POSIX): * for every value, numbers, ranges (1-5), lists (1,15,30), steps (*/10, 1-30/5, 5/15 meaning from 5 to the end), month and weekday names (JAN-DEC, SUN-SAT), 0 or 7 for Sunday, ? as another spelling of *, an optional leading seconds field as used by Quartz and Spring, and the macros @hourly, @daily, @midnight, @weekly, @monthly, @yearly and @annually. The Quartz extensions L, W and # are refused with a message rather than guessed, and @reboot has no schedule. Full-width digits, letters, symbols and spaces typed with a Chinese, Japanese or Korean input method, and Chinese commas, are read as cron's own half-width characters; a note under the sentence shows the expression as cron itself needs it.

The job runs when either matches, as in Vixie cron: 0 0 1 * 1 runs on the first of every month and on every Monday. Vixie cron makes one exception, and so does this tool: a field that starts with *, such as */2, does not count as set, and the job then runs only on days that match both, so 0 0 */2 * 1 runs on odd-numbered days that are Mondays. The tool says which rule applies under the sentence, because this is the rule most people get wrong.

Runs are computed in the zone you pick using the browser's own IANA zone database. A time that does not exist on a spring-forward day (02:30 when clocks jump from 02:00 to 03:00) is skipped that day; a time that happens twice on a fall-back day runs once, at the first occurrence. The run list marks both: a skipped time gets a row of its own, and a run whose time happens twice says so. Cron daemons differ here: some run the skipped job right after the jump, so check your own daemon's manual for critical jobs. Each run also shows its UTC instant.

Five years: until the same date and time five years from now, counted in UTC (from 29 February, until 1 March), a run at that very moment included. When fewer runs than you asked for fall inside, it says how many; when none does, it says so instead of listing nothing. 0 0 29 2 */7, midnight on a 29 February that is a Sunday (2032, then 2060), is such a case from most dates. Day 31 in a month without one is skipped for that month; an expression whose day can never occur in its months (0 0 31 4 *) is refused as never running.

No. The page loads a small script into your browser and every calculation runs on your device. You can check this yourself in the browser's network panel: after the page has loaded there are no upload requests. Closing the tab discards what you entered.

No. These basic tools are free, have no limits set by us and store nothing on our servers.

Nothing you open or type. While the tab is open, the tool pages keep a short list of the steps taken in it, in the tab's session storage: the step (page opened, started, succeeded, first success, used again or failed), the tool's name, the time, how many files were used and, for a failure, an error code; never a file name, the contents of a file or your text. It holds at most the latest 200 steps, and the browser deletes it when the tab closes. The page never sends it. Where a Report a problem button is shown, you can attach the last 20 steps to your report; nothing is attached unless you tick that box. In local storage the page keeps only choices you made: a Light or Dark theme until you choose System again, the language you picked with the EN / 中文 switch if it differs from your browser's language, and this tool in your recently used list if you switched that list on at the tools page.