Cron Expression Builder

Frequently Asked Questions

What cron format is used?

Standard 5-field Unix crontab: minute, hour, day-of-month, month, day-of-week. Supports every operator you would expect: * (any), */N (every N), ranges like 1-5, lists like 1,3,5, and combinations like */2,15-20. This is the same format used by Unix crontab, Kubernetes CronJob, GitHub Actions, GitLab CI, and AWS EventBridge.

Are seconds supported?

No. This is a 5-field tool. 6-field cron (with a leading seconds column) is a Quartz / Spring-specific extension used by Java schedulers. If you are editing a Spring @Scheduled or a Quartz job, most schedulers accept the 5-field form with an implicit 0 seconds.

How are the next run times calculated?

Using the same logic as the standard cron-parser library: the tool steps forward from now, field by field, until it finds the next timestamp that matches. Times are shown in your browser's local timezone; change the clock's timezone in your OS and refresh to see them in UTC.

What's the difference between 0 0 * * 1-5 and */5 9-17 * * 1-5?

The first fires at midnight Monday–Friday (five times a week). The second fires every 5 minutes from 09:00 to 17:00 Monday–Friday (≈ 600 times a week). Always read your cron expressions out loud in English. The tool's human-readable line will catch most mistakes before they reach production.

Why does my schedule run twice as often as I expected?

The classic trap: when both day-of-month and day-of-week are restricted, standard cron runs if EITHER matches, not both. `0 0 15 * 1` means "midnight on the 15th OR midnight on any Monday", not "only Mondays that fall on the 15th". Leave one of the two fields as * to get a single condition.

Does this work for Kubernetes CronJob / GitHub Actions / GitLab CI?

Yes. All three use the standard 5-field format this tool generates. One thing to double-check: GitHub Actions runs on UTC regardless of where your repo lives, so "0 9 * * *" in a GitHub workflow fires at 9:00 UTC, not 9:00 local.

Is the cron expression sent anywhere?

No. The parsing, validation and next-run calculation all run as JavaScript in your browser tab. The DevTools Network tab confirms no outbound request fires. Nothing is stored or logged.

How do I write a cron expression that runs on the last day of the month?

Standard 5-field cron does not have an "L" (last) operator; that is a Quartz / Spring extension. To run on the actual last day of every month with standard cron, you cannot do it in a single expression. The usual workaround is to run on the 28th, 29th, 30th and 31st with a script that checks `[ "$(date -d tomorrow +%d)" -eq 1 ] && do-the-job`. On Quartz / Spring (`@Scheduled`) you can write `0 0 0 L * ?` directly.

What's the difference between 0 */2 * * * and 0 0,2,4,6,8,10,12,14,16,18,20,22 * * *?

They are identical: both fire every two hours at minute 0. The `*/2` form is shorthand for "every 2nd value starting from 0". For odd starting offsets (e.g. "every 2 hours starting at 1am") you need the explicit list form `0 1,3,5,7,9,11,13,15,17,19,21,23 * * *`, because */2 always starts from 0.

Can I use month names and weekday names instead of numbers?

In most schedulers yes: JAN-DEC for months, SUN-SAT for weekdays, case-insensitive, so `0 9 * * MON-FRI` means the same as `0 9 * * 1-5`. AWS EventBridge requires the name form for weekdays. This editor validates digits and the operators * - / , only, so type `0 9 * * 1-5` here; numeric form is the safer choice across platforms anyway.