Cron Expression Builder
Build five-field Unix cron schedules, check expressions and preview upcoming runs in an explicit timezone.
Schedule
Timezone is a preview setting, not part of the expression. Uses your browser’s local zone initially; enter an IANA zone or UTC.
Restrict months (optional)
Use your device’s multiple-selection controls. On desktop, Ctrl/Command adds or removes a selection.
Choose a builder setting or enter an expression, then preview.
Five fields, one schedule.
Order: minute (0–59), hour (0–23), day of month (1–31), month (1–12), day of week (0–7; both 0 and 7 mean Sunday). Use numeric values, * for all values, ascending ranges, comma lists and /steps. Names, seconds, commands, @presets, L, W, #, ? and hashed schedules are not supported.
0 9 * * 1-5 means 09:00 Monday through Friday. Steps restart within their field: */17 means minutes 0, 17, 34 and 51 of each hour, not a continuous 17-minute interval. When both day fields are restricted, Unix cron matches either day, not both.
Build or edit.
Common schedules synchronize with the builder. Advanced expressions remain manual; changing a builder control explicitly replaces them. Month and day selectors support multiple selection. Select at least one day for a selected-day schedule.
Timezone belongs to the preview.
The five-field expression contains no timezone. The preview starts after you click Preview and uses the displayed IANA timezone. The host scheduler needs its own timezone configuration. This tool previews data; it does not install or execute scheduled commands.
Run calculations use cron-parser and your browser’s timezone data. For the tested New York spring transition, 02:30 moves to 03:30; the repeated 01:30 in autumn is emitted once, at its first occurrence. DST gap and repeated-hour behavior varies among cron daemons; compare the preview with your deployment scheduler. This is not Quartz, AWS EventBridge or systemd syntax.
Local and bounded.
Expressions are limited to 256 characters. Five runs are computed in a terminable local worker with a 2-second processing deadline and 5-second startup deadline. Complex or impossible schedules fail safely. Input and output stay in memory and clear on reset or navigation; nothing is uploaded, logged or saved.