Cron Expression Parser

Cron Expression Parser takes a 5-field cron expression or a preset (@hourly, @daily, @weekly, @monthly, @yearly, @reboot) and renders a human-readable summary, a per-field breakdown, and the next 5 fire times.

The fields

Standard cron has 5 whitespace-separated fields — minute hour day-of-month month day-of-week. Each field accepts:

• * — any value
• N — a literal number
• N-M — a range
• N,M — a list
• */N — step (every N)
• A-B/N — range with step

Quick presets

• @hourly — 0 * * * * (at minute 0 of every hour)
• @daily — 0 0 * * * (midnight every day)
• @weekly — 0 0 * * 0 (Sunday midnight)
• @monthly — 0 0 1 * * (1st of the month at midnight)
• @yearly — 0 0 1 1 * (Jan 1 at midnight)
• @reboot — runs once at startup

Examples

• */15 9-17 * * 1-5 — every 15 minutes during 9:00–17:59, weekdays only.
• 30 2 1 * * — at 02:30 on the 1st of every month.
• 0 0,12 * * * — at midnight and noon every day.
• 0 17 * * 5 — at 17:00 every Friday.

Day-of-month vs day-of-week

In most cron implementations both fields can trigger a day; our parser follows the common convention where both conditions are OR-combined (a day-of-month OR a day-of-week hit can both fire). This is what most production schedulers do in practice.

About the next fires preview

We project forward up to 5 years looking for matches. For tight expressions (* * * * *) you’ll see the next 5 minutes; for sparse ones (0 0 1 1 *) you might see the next 5 New Year’s Days.

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