Cron Explainer
Read a five-field cron expression back in plain English and see the next run times, so you can check a schedule before it goes live.
Five fields: minute, hour, day of month, month, day of week.
Two behaviours that surprise people
When both day of month and day of week are restricted, standard cron runs the job
if either matches, not both. So 0 0 13 * 5 fires on
every Friday and on the 13th of every month, which is almost never what the author
meant. The explanation below spells this out when it applies.
Times are worked out in your machine's local timezone, which is what your own
crontab uses unless CRON_TZ or the system timezone says otherwise.
A server in UTC will fire at different wall-clock times, and a schedule inside the
daylight-saving transition either runs twice or not at all.