Cron Expression Helper — What this calculator does
This calculator takes a classic 5-field cron expression and converts it into a human-readable schedule.
It also computes the next N run times starting from a chosen date/time and timezone, and presents the schedule
visually on a mini calendar and a timeline.
Cron format supported
The calculator supports the standard 5-field form:
The calculator is intentionally “basic and safe”: it supports the common operators
*, lists (1,2,3), ranges (1-5), and steps (*/10, 1-10/2).
Advanced extensions like L, W, #, and ? are not included.
Optional macros
If enabled, some common macros are recognized and expanded to 5-field equivalents:
@hourly → 0 * * * *@daily (or @midnight) → 0 0 * * *@weekly → 0 0 * * 0@monthly → 0 0 1 * *@yearly (or @annually) → 0 0 1 1 *
Timezone and “next run times”
Cron schedules depend on timezone. The same expression can produce different run times if evaluated in different
timezones, especially around daylight saving time (DST). This calculator evaluates the schedule using the selected
timezone and then lists the next N occurrences starting from the chosen start date/time.
When DST changes occur, some local times may be skipped or repeated. The calculator follows the browser’s timezone rules
for the selected zone.
DOM + DOW nuance (important)
A well-known cron nuance appears when both day-of-month (DOM) and day-of-week (DOW) are restricted (not *).
Different cron implementations handle this differently:
- OR semantics (common): run when DOM matches or DOW matches.
- AND semantics (some systems): run only when DOM matches and DOW matches.
Because this behavior varies, the calculator lets you choose the semantics so the results match the cron flavor you are targeting.
What the outputs mean
-
Human-readable description — an English interpretation of the fields (for example, “At 04:30 on weekdays…”).
-
Next run times — a chronological list of the next N occurrences (formatted in the selected timezone).
You can copy this list or export it as CSV.
-
Field breakdown — each field’s raw input and the expanded set of allowed values (truncated if very large).
-
Warnings — invalid ranges/steps, macro expansions, DOM+DOW nuance messages, or safety limits reached.
Visualizations
-
Mini calendar — highlights the days in the displayed month that contain at least one upcoming run.
Stronger highlight indicates multiple runs on that day.
-
Timeline — places the next N runs along a horizontal time axis from the first to the last run, helping you see clustering
and spacing patterns.
Typical examples
0 9 * * 1-5 → every weekday at 09:00*/15 8-17 * * 1-5 → every 15 minutes during business hours on weekdays30 4 1 * * → at 04:30 on the first day of every month
This tool is meant for understanding schedules and previewing upcoming run times. Always confirm behavior against the cron
implementation you will actually use, especially for DOM+DOW semantics and DST boundaries.
