Cron Expression Builder

Cron is the time-based job scheduler that has run the world's servers since 1975. If you've ever automated a nightly backup, scheduled a report, cleared a cache, or triggered a newsletter, you've written — or fought with — a cron expression. The syntax is compact, powerful, and famously easy to get wrong. This tool builds and explains cron expressions so you can schedule with confidence instead of guessing and redeploying.

How a cron expression is structured

A standard Unix cron expression has five fields, separated by spaces: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–6, where 0 is Sunday). A value of `*` means "every". So `0 9 * * 1-5` reads as "at minute 0 of hour 9, every day, every month, but only Monday through Friday" — i.e. 9:00 AM on weekdays.

The operators that do the real work

- `*` — every value in the field - `,` — a list, e.g. `1,15` (the 1st and 15th) - `-` — a range, e.g. `1-5` (Monday to Friday) - `/` — a step, e.g. `*/15` in the minute field means "every 15 minutes"

Combining them covers almost every schedule: `*/30 9-17 * * 1-5` runs every 30 minutes during business hours on weekdays.

Five fields or six?

Classic Unix cron uses five fields and has no concept of seconds. Quartz, Spring, and many modern schedulers add a sixth leading field for seconds (and sometimes a seventh for year). This tool supports both — toggle the mode to match your platform, because pasting a six-field expression into a five-field parser is one of the most common scheduling bugs.

Why timezones bite

Cron runs in the server's local timezone. A job set for "midnight" runs at midnight wherever the machine thinks it is — which on most cloud servers is UTC, not your local time. Always confirm the server's timezone before trusting a schedule, and remember that daylight-saving transitions can silently skip or repeat an hour.

Common schedules to copy

- Every minute: `* * * * *` - Every hour on the hour: `0 * * * *` - Every day at 2:30 AM: `30 2 * * *` - Every Monday at 8 AM: `0 8 * * 1` - First day of every month: `0 0 1 * *`