Cron Expression Parser
The cron parser reads a five-field crontab expression, describes in plain English when it fires, and lists the next run times in UTC. It expands ranges, steps and names, understands the @daily style shorthands, and warns about the day-of-month and day-of-week rule that catches almost everyone out.
Cron expression
Schedule
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How to use the Cron Expression Parser
- Paste the cron expression — five fields separated by spaces: minute, hour, day of month, month, day of week.
- Read the plain-English description at the top.
- Check the next run times, which are shown in UTC.
- Choose how many upcoming runs to list if you need to see the pattern.
Example
Input
30 2 * * 1-5
Output
At 02:30, on Monday, Tuesday, Wednesday, Thursday, Friday.
Common use cases
- Checking that a schedule you wrote fires when you intended.
- Understanding an inherited crontab entry before changing it.
- Confirming a job will not fire more often than you expect.
- Working out when a nightly job will next run relative to a deploy.
Limitations and things to watch for
- Run times are calculated in UTC. Your server runs cron in its own time zone, so the actual local firing time may differ, and daylight saving transitions can cause a job to be skipped or repeated.
- Only the standard five fields are read. Six-field expressions with a leading seconds field, used by Quartz and some libraries, are rejected rather than misread.
- Non-standard extensions such as L (last), W (weekday) and # (nth weekday), supported by Quartz but not by Vixie cron, are not understood.
Frequently asked questions
Why does my job run more often than I expect?
Usually because both the day-of-month and day-of-week fields are restricted. Cron treats those two as OR, not AND — so 0 0 1 * 1 fires on the 1st of the month and on every Monday, not only on a Monday that falls on the 1st.
What does */15 mean?
Every 15 units within that field, starting at its lowest value. In the minute field that is 0, 15, 30 and 45 — so four times an hour, not every 15 minutes from whenever the job last ran.
Which time zone are the next runs in?
UTC. Cron itself uses the server's local time zone, so if your server is not on UTC, shift the times accordingly. This also means a schedule can be skipped or repeated at a daylight saving transition.
Are @daily and @reboot supported?
@yearly, @annually, @monthly, @weekly, @daily, @midnight and @hourly are expanded to their equivalent expressions. @reboot is not, because it has no schedule — it fires once when cron starts.
Why was my expression rejected as having six fields?
Some schedulers, notably Quartz and several libraries, prepend a seconds field. This parser reads standard five-field crontab syntax, so it reports the mismatch rather than silently misinterpreting every field.