What does this cron expression actually do?
Paste a crontab line to get it in plain English, field by field, plus the next five times it will fire — so a misplaced asterisk is obvious before it reaches production.
—
—Field by field
Next five runs
Three cron behaviours that cause real incidents.
Day-of-month and weekday are OR, not AND
If both fields are restricted, cron runs when EITHER matches. “0 0 13 * 5” fires on the 13th and on every Friday — not only on Friday the 13th. This surprises almost everyone once.
It runs in the server’s timezone
Cron uses the system timezone unless CRON_TZ or TZ is set in the crontab. Daylight saving can make a job run twice or not at all on the changeover day.
Ranges with steps start at the range beginning
“0-30/10” gives 0, 10, 20, 30 — not 10, 20, 30. And “*/7” on minutes gives 0, 7, 14 … 56, then jumps back to 0, so the gap across the hour boundary is only 4 minutes.
Check something else
Found something you’d rather not fix yourself?
Configuring DNS, TLS and email authentication properly — without breaking live traffic — is part of our cybersecurity and managed services work.