~/tools$ ./use
Explain any crontab line in plain English. Paste a standard 5-field cron expression or a named macro like @daily and instantly read what it fires on, see each field expanded into its values, and view the next five run times. No sign-up.
The Vixie 5-field format — minute, hour, day of month, month and day of week — with ranges (1-5), steps (*/15), lists (1,15), month names (JAN-DEC) and weekday names (SUN-SAT), plus the standard macros like @daily and @hourly. @reboot is intentionally not supported.
Exactly like cron does: when both fields are restricted, a run fires when either one matches. That is why `0 0 13 * 5` includes both every Friday and the 13th of every month.