Cron expression explainer

Good to know

The five fields

Minute (0–59), hour (0–23), day of month (1–31), month (1–12 or JAN–DEC) and day of week (0–7 or SUN–SAT, where both 0 and 7 are Sunday). * means every value, */n every n-th, a-b a range, and commas list values.

Day of month and day of week together

When both are set, cron runs when either matches. “0 0 13 * 5” runs on the 13th and on every Friday, not only on Friday the 13th.

Know when a cron job silently stops

Cron doesn't tell you when a job fails or never runs. Spot Downtime's heartbeat monitors give each job a URL to ping when it finishes, and alert you if the ping doesn't arrive.