Cron Explainer

About this cron expression explainer

A standard cron expression has five fields, in the order minute hour day-of-month month day-of-week. Each field is a list of values separated by commas, a range written with a hyphen, a step written after a slash, or a star meaning "every". So */15 9-17 * * MON-FRI means every fifteen minutes, during the hours 9 to 17, on weekdays. The day-of-week field accepts 0–6 with 0 as Sunday, and the names SUN to SAT; the month field accepts 1–12 and JAN to DEC.

The subtle rule that catches almost everyone is the interaction between day-of-month and day-of-week. When both are restricted to specific values, cron does not require both to match — it fires when either matches. So 0 0 13 * FRI runs on the 13th of the month and on every Friday, not only on Friday the 13th. If you need "Friday the 13th", you have to enforce the second condition in the job itself. The breakdown table above flags this case whenever it applies.

Two boundaries are worth stating. This tool implements the classic five-field form; Quartz-style six-field expressions with a leading seconds column, and the non-standard ? character, are not accepted. It also evaluates schedules in your local timezone, because that is what a cron daemon on a server you are logged into would do — a job defined as "daily at 09:00" runs at 09:00 local, not 09:00 UTC, unless the daemon has been configured otherwise.