Cron Schedule Explainer & Humanizer

Patterns worth knowing

The five fields are minute, hour, day of month, month, and day of week. */15 * * * * runs every 15 minutes, 0 9 * * 1-5 at 09:00 on weekdays, 0 0 1 * * at midnight on the first of each month, and 30 2 * * 0 at 02:30 every Sunday.

One rule surprises nearly everyone: when both day of month and day of week are restricted, the job runs when either matches. 0 0 13 * 5 runs on every 13th and on every Friday, not only on Friday the 13th.

Time zones and platform differences

Cron runs in the time zone of the machine or service, often UTC. Where the zone has daylight saving, a job between about 01:00 and 03:00 can be skipped or run twice on the nights clocks change. Schedule outside that window, or run in UTC.

Not every scheduler reads the same syntax. GitHub Actions uses standard five-field cron in UTC. AWS EventBridge adds a year field and uses ? in one of the day fields. Quartz and Spring add a seconds field at the start. Check what your platform expects before copying an expression across.

How to use it

1. Type or paste a 5-field cron expression (e.g. */15 9-17 * * 1-5).
2. Review the plain-English schedule explanation.
3. Inspect the next 10 calculated execution timestamps.

Privacy & limitations

Parsing runs locally in your browser.