A cron expression is a 5-field schedule used by crontab and many job schedulers: minute (0-59), hour (0-23), day of month (1-31), month (1-12) and day of week (0-7, where both 0 and 7 mean Sunday). This parser supports the standard syntax: * for any value, comma lists (1,15), ranges (9-17) and steps (*/5 or 0-30/10). Following classic cron rules, when both the day-of-month and day-of-week fields are restricted the job runs if either one matches.
Besides explaining each field in plain language, the tool computes the next 5 run times by scanning forward minute by minute from now (up to 4 years) in your local timezone, so what you see is exactly when the job would fire on a machine set to your clock. Everything runs locally in your browser; the expression is never uploaded.