Check a cron expression
Paste a cron expression to see the next five runs as real timestamps, in the timezone you choose. Catches the expressions that parse but fire far more often than intended.
What it checks
- Field count: five fields, or six when the first one is seconds.
- The next five runs as ISO timestamps.
- The gap between runs, flagged when a job restarts every minute and can overlap itself.
- Timezone: which zone the runs are computed in, and a warning when none is set.
- Expressions that never match any date, such as 30 February.
- Common traps: five wildcards, or a minute-only field that fires hourly rather than daily.
What is not stored
Nothing is stored and nothing is sent. This checker is JavaScript that runs inside your browser tab, so the value you paste never reaches h2check.org or any other server. Close the tab and it is gone.
Limits
- Dialects differ. Quartz, AWS EventBridge and Kubernetes CronJob each reject syntax the others accept. This parser follows the Unix and node-cron rules.
- Non-standard names such as @reboot are not supported.
- A schedule that is correct here can still drift on a host whose clock or timezone differs from the one you picked.
Procedures that explain the result
- How to check cron schedule drift
- How to check if a cron job is still running
- How to validate cron expression
- Why is my cron job not running
Put it on your own page
Link to it with the value filled in, and the checker runs as soon as the page opens.
<a href="https://h2check.org/tools/cron/">Check a cron expression</a>