Cron Expression Builder

Cron has been scheduling jobs on Unix systems since the 1970s, and its five-field syntax — minute, hour, day of month, month, weekday — has barely changed since. That terseness is also why cron mistakes are so common: a schedule that looks right can silently run at midnight UTC instead of 9am local, or fire far more often than intended. This tool works in both directions: type an expression to have it decoded, or build one field-by-field.

As you type, the expression is parsed and translated into plain English ("At 9:00 AM, weekdays (Mon–Fri)"), and any invalid field produces a specific error — an out-of-range value, a backwards range, a malformed step. The visual builder gives each field its own input with one-tap quick values, and fourteen presets cover the schedules people actually use, from every five minutes to quarterly.

The most useful part is the next-run preview: the tool computes the next five times your schedule will fire, shown in your local timezone or UTC (one click to toggle) with relative countdowns. This catches the classic surprises before they reach a server — timezone offsets, an impossible date combination like February 30th that never fires at all, or the day-of-month/weekday OR rule quietly doubling your run frequency.

It supports the full standard crontab grammar: * wildcards, comma lists, ranges with -, step values with /, and names like MON or JAN. When both day-of-month and weekday are restricted, they combine with OR, exactly as classic Vixie cron does.