Cron Expression Syntax Reference

Traditional cron uses five space-separated time fields. Verify the exact scheduler dialect before deployment because cloud services and libraries may add seconds, years, macros, or different day rules.

Five-field layout

┌ minute        0–59
│ ┌ hour        0–23
│ │ ┌ day       1–31
│ │ │ ┌ month   1–12
│ │ │ │ ┌ weekday 0–7 (Sunday commonly 0 or 7)
│ │ │ │ │
* * * * *

Operators

An asterisk selects every allowed value. A comma forms a list such as 1,15. A hyphen creates an inclusive range such as 1-5. A slash applies a step such as */10 or 5-55/10. The step advances within the field's selected range; it is not a duration measured from the last successful run.

Day-of-month and day-of-week

When both day fields are restricted, traditional cron implementations often run when either field matches, but dialects differ. Some schedulers require a placeholder in one field, while others combine conditions differently. Test expressions such as 0 9 1 * 1 in the actual platform rather than assuming it means “the first day of the month when it is Monday.”

Time zones and daylight saving time

The scheduler may use the machine timezone, UTC, an account setting, or a timezone attached to the job. Record it explicitly in deployment configuration. During daylight saving transitions, a local time can be skipped or occur twice. Use UTC for invariant intervals, or make local-time jobs idempotent and able to tolerate missing or repeated wall-clock occurrences.

Scheduler dialect differences

Quartz-style cron often includes a seconds field and may support characters such as ?, L, W, and #. Cloud schedulers can use six fields, year fields, named months, macros, or rate expressions. A valid expression in one product may be rejected or mean something different in another. Confirm field count, ranges, day behavior, timezone, and minimum frequency from the platform documentation.

Operational safety

A cron schedule only triggers work; it does not guarantee that the previous run finished. Protect jobs against overlap with a lock, lease, or queue when concurrent execution is unsafe. Make processing idempotent, persist progress, bound retries, and expose duration and failure metrics. Add jitter when many tenants or services would otherwise start expensive work at exactly midnight.

Validate next run times

Before deployment, calculate several upcoming runs across month boundaries and a daylight saving transition for the configured timezone. Confirm that the scheduler uses the expected dialect. Build and preview five-field expressions locally with the Cron Expression Builder.

Frequently Asked Questions

Related Tools and Guides