CronProbe — Crontab Syntax Checker & Schedule Visualizer

Cron Expression Checker 100% CLIENT-SIDE

Cron Expression (5 fields, or an @special)

Human Translation & Next Runs

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Frequently Asked Questions

Is my data safe on cronprobe.net?

Yes. Cron expressions are parsed in your browser. Nothing is sent to a server.

What does 0 */6 * * * mean?

Minute 0 of every 6th hour: 00:00, 06:00, 12:00, and 18:00, daily. The step operator */6 applies to the hour field, so it counts from 0 rather than from the current time.

How do I see when a cron job will actually run next?

Enter the expression and the schedule visualizer expands each field into plain English and lists the upcoming run times. Day-of-month and day-of-week are OR-ed together when both are restricted, which is the most common source of surprise runs.

🧭 Pro Tips & Gotchas

What it checks

Five whitespace-separated fields are parsed and labelled individually: minute, hour, day-of-month, month, day-of-week. A sixth leading field (seconds, Quartz-style) is rejected here — standard cron is five.
The breakdown shows each field's expansion, so */15 reveals itself as four hits per hour instead of staying cryptic.
Next-run times are computed here with Vixie-cron rules and reported in your browser's time zone, which the output names. If your server runs a different zone, use the time-zone page to evaluate the schedule there: a schedule evaluated in a DST-observing zone can skip or double-run on transition days.

Cron gotchas that cost real money

Day-of-month and day-of-week are OR'd in classic Vixie cron: 0 9 1 * 5 fires on the 1st and every Friday, not "the first Friday". And 1-5 is inclusive on both ends. This checker applies that OR rule and warns you when both day fields are restricted.
Both day fields constrained is the classic monthly-report bug. If you need "first Friday only", gate inside the job instead of the schedule.
@reboot does not mean what people hope on laptops and containers: it means the host rebooted, not the service started. Use systemd WantedBy=timer or an entrypoint hook.
Fallback if you need a missing special string: @daily is exactly 0 0 , @weekly is 0 0 0, @monthly is 0 0 1 , @yearly/@annually is 0 0 1 1 .
DST: a job at 3:30 may run twice on fall-back or not at all on spring-forward, depending on the scheduler. Schedule in UTC (CRON_TZ=UTC / TZ=UTC) or accept the drift.
0 0 29 2 is never satisfied in non-leap years; 0 0 2-4 and 0 0 * 7 behave differently across implementations (7 is Sunday in most, rejected by some).
Overlapping runs are the default. Wrap real work in flock -n /tmp/job.lock command... so a slow run cannot stack against the next tick.
Cron's PATH is minimal and MAILTO is usually unset, so a job that works in your shell fails with "command not found". Use absolute paths and log explicitly.