Cron Evaluator - evaluate when a cron expression runs

Field validation happens first. The evaluator checks field count, token syntax, and ranges before calculating future matches, then highlights the field behind a humanized parser error.

Paste the cron to validate it, read its English meaning, list five future matches, and inspect runs in a navigable month calendar. The mobile agenda shows up to 30 runs from the visible month.

No. The five-run evaluator starts from now; the page has no arbitrary start-date control. The month calendar can navigate to other months and computes that visible month's runs separately.

Yes. The multi-cron visualizer plots the visible month's runs together and automatically lists up to five expression pairs that fire in the same minute.

Only a limited static check reports “never” for fixed day/month combinations. 0 0 30 2 * qualifies because February 30 cannot exist; zero matcher results alone do not prove that outcome. Expression: 0 0 30 2 *

Yes. 0 0 29 2 * evaluates only on February 29 in leap years, so expect long gaps between displayed runs. Expression: 0 0 29 2 *

In Standard Vixie semantics, two restricted day fields are ORed. 0 9 1 * 1 evaluates on every Monday and every first day of a month. Expression: 0 9 1 * 1

A day-of-month step restarts at day 1 each month. 0 0 */7 * * selects dates 1, 8, 15, 22, and 29 rather than preserving a seven-day elapsed gap. Expression: 0 0 */7 * *

0 0 9 ? * MON#2 evaluates to 09:00:00 on the second Monday of each month in a Quartz-style extended dialect. Expression: 0 0 9 ? * MON#2

The selected IANA timezone supplies the clock for next-run timestamps and the calendar. Match it to your scheduler, because Vercel uses UTC while other platforms expose timezone settings.

Evaluate a fixed 01:00-03:00 local schedule across the transition. A spring-forward time may not exist, while a fall-back time may occur twice under Vixie cron. Expression: 30 2 * * *

It can preview many extended forms, but Extended mode is not a dialect validator and does not enforce every AWS or Quartz rule. Use Copy as and the dialect matrix, then test with the target scheduler.

CronTool uses @datasert/cronjs-parser and @datasert/cronjs-matcher with a 1,000-iteration cap. It is a preview, not an emulator for every scheduler; verify dialect rules and DST behavior against the production target.

Share cron=<expression>, add mode=extended when needed, and add tz=<IANA zone> for matching timestamps. The built-in Copy link does not preserve timezone.

Runtime execution remains outside evaluation. CronTool cannot inspect PATH, environment variables, permissions, host downtime, queueing, overlap, or command success, and it does not run commands.