Cron Expression Explainer

How to use

1. Type or paste a five-field cron expression, or pick a common schedule.
2. Read the plain-English explanation and the meaning of each field.
3. Check the next run times, switching to UTC if your server runs in UTC.

What this tool does

A cron expression has five fields: minute, hour, day of month, month and day of week. Each field accepts a number, a list (1,15), a range (1-5), a step (*/10) or a name (MON, JAN). The explainer follows the rules used by the standard Linux cron daemons (Vixie cron and cronie), including the rule that when both the day-of-month and day-of-week fields are restricted, the job runs when either one matches.

Why it matters

Cron syntax is compact and easy to misread. A schedule meant for “9am on weekdays” that actually runs every minute between 9 and 10 can overload a server or send hundreds of emails.

Example

30 2 * * 1-5 means “At 02:30, on Monday through Friday”. */15 9-17 * * * means every 15 minutes during the hours 09:00 to 17:59.

Common uses

• Checking a server crontab line before saving it.
• Replacing WordPress’s visitor-triggered WP-Cron with a real server cron job that calls wp-cron.php.
• Understanding schedules in hosting panels, CI pipelines and backup tools.

Tips

• Cron runs in the server’s time zone, which is often UTC. Tick “Show times in UTC” to match.
• To run WP-Cron from the server, add define( ‘DISABLE_WP_CRON’, true ); to wp-config.php and schedule */5 * * * * to request wp-cron.php.
• Avoid scheduling every heavy job at minute 0; spread them out to reduce load spikes.

Limitations

• Standard five-field cron only. Quartz and Spring formats (seconds field, ?, L, W, #) are explained as unsupported rather than guessed.
• Around daylight-saving changes, cron daemons differ in how they handle skipped or repeated hours. Times that do not exist locally are left out of the list.
• WordPress’s internal WP-Cron uses intervals (hourly, twicedaily, daily), not cron expressions, and only runs when someone visits the site.

Troubleshooting

• “Found 6 fields”: remove the seconds field at the start (Quartz) or the year at the end.
• A job never runs: check that day 31 or 30 exists in the months you selected, and that the server time zone is what you expect.