developer desk · cron explainer
A cron expression in words, and when it will really run.
Type a cron expression to read it in plain English and see its next runs in any time zone — with the nights the clocks change marked on the runs they move. Computed in this tab.
Most explainers list runs in UTC or in your own zone and say nothing about daylight saving. A job at 02:30 in Berlin does not run at 02:30 on the last Sunday of March — this page says so on that run.
Once the schedule is right
Jobs that write rows often need an id; a v7 UUID sorts by the time it was made.
Generate UUIDsQuestions
What happens to a 02:30 job when the clocks change?
In spring, 02:30 does not exist in zones that jump from 02:00 to 03:00, and the page shows where this engine runs it instead. In autumn, 02:30 happens twice; it runs once. Schedulers differ here, which is why the page marks those runs instead of hiding them.
Which cron syntax does it read?
Standard five-field cron, an optional sixth seconds field at the front, ranges, steps, lists, names such as MON and JAN, and shortcuts such as @daily and @hourly. When both day of month and day of week are set, a day matching either one runs, as in classic cron.
Why does it say the expression never fires?
Because no date satisfies every field — the thirty-first of February, for example. A scheduler would accept it and silently never run it.