Paste a five-field crontab schedule — or one of the @ macros — and the tool reads it back: each field explained in plain language with the exact set of values it matches, the next five occurrences, and the dialect's footguns flagged as you type.
The five fields
minute hour day-of-month month day-of-week, with ranges a-b, lists a,b, steps */n and a-b/n, and names (JAN–DEC, SUN–SAT). The @ macros — @yearly, @monthly, @weekly, @daily, @hourly and friends — expand to their five-field forms; @reboot has no schedule at all, and the tool says so instead of inventing one.
The footguns it flags
The big one: when day-of-month and day-of-week are both restricted, cron runs the command when either matches — an OR, not the AND almost everyone expects. Also: 0 and 7 are both Sunday; a step that does not divide its span evenly wraps ragged (*/7 in minutes ends at 56, then jumps to 0); names inside stepped ranges are historically unreliable across implementations; and a six-field input is recognized as Quartz's seconds dialect and named as such.
About the projected times
cron evaluates schedules in the daemon's local time. The occurrences here are computed on the wall-clock of your browser's current instant, with no time-zone database applied — the same deterministic engine the golden vectors pin against a frozen reference moment.
Everything runs locally; the schedule never leaves the page. Grounded in crontab(5) and the POSIX specification.