What Is a Cron Expression?
A cron expression describes a recurring schedule with compact fields for minute, hour, day of month, month, and day of week. The standard five-field expression 0 9 * * 1-5 means 9:00 AM from Monday through Friday.
Some libraries add a leading seconds field, producing a six-field expression. That extension is useful in compatible application schedulers, but it is not interchangeable with POSIX crontab, GitHub Actions, or Kubernetes CronJob schedules.
How to Build a Cron Schedule
- Choose a preset or select each cron field in the visual builder.
- Pick the timezone used by the target scheduler and review the previous and next run times.
- Copy the generic expression or a compatible GitHub Actions or Kubernetes snippet.
Raw mode accepts expressions supported by the parser. Syncing to visual mode is intentionally limited to syntax the controls can preserve without changing its meaning.
Five Fields vs Six Fields
| Target | Fields | Timezone |
|---|---|---|
| POSIX crontab | 5 schedule fields | Implementation or system setting |
| GitHub Actions | 5 fields | UTC by default; IANA timezone supported |
| Kubernetes CronJob | 5 fields | .spec.timeZone |
| Compatible libraries | Often 5 or 6 | Library-specific |
Timezone and DST Behavior
Cron fields represent wall-clock time in the scheduler’s timezone. Selecting the correct IANA timezone matters because daylight-saving transitions can skip a local time or make it occur twice. The preview formats every run in the selected zone and also stores its unambiguous UTC ISO timestamp in the downloaded report.
If both day-of-month and day-of-week are restricted, traditional cron implementations commonly match when either field matches. For predictable schedules, restrict one of those fields and leave the other as * unless the target scheduler documents different semantics.
Related Scheduling and Developer Tools
Compare dates across regions with the Time Zone Converter, inspect epoch values with the Unix Timestamp Converter, format infrastructure configuration using the JSON Formatter, or test validation patterns with the Regex Tester.