Cron Tester - validate any cron expression online

It checks Datasert parser syntax and ranges, shows humanized field errors, runs CronTool's lint rules, and statically detects some impossible fixed day/month combinations. It does not fully validate a selected scheduler dialect.

Validation is purely syntactic - the parser accepts or rejects the string. Testing goes further: it computes the next runs, projects them onto a calendar, and lets you eyeball whether the schedule actually matches your intent. CronTool does both in real time as you type.

It highlights the offending field and gives a humanized range message. Minute 60, hour 24, day-of-month 32, and month 13 all fail validation.

The lint reports that it looks like an extended cron and offers to switch modes. It withholds other lint advice until the field shape is no longer ambiguous.

It adds an informational lint at 288 runs per day and a warning at 1,440 or more, noting that many hosts rate-limit schedules at those densities. Expression: * * * * *

0 9 1 * 1 triggers the warning in Standard mode. The lint says Vixie cron fires on day 1 and every Monday because it ORs restricted day fields. Expression: 0 9 1 * 1

Yes. A day-of-month step above one warns that steps restart at day 1 each month; a month step warns that it restarts at January. Expression: 0 0 */2 * *

It proves only fixed day/month impossibilities, such as 0 0 30 2 *. Steps and special operators bypass that static proof, and zero results from the capped matcher do not receive a never-fires verdict. Expression: 0 0 30 2 *

For fixed 01:00-03:00 schedules, it warns when the selected timezone has a transition within 60 days and says whether the hour may be skipped or repeated. Expression: 30 2 * * *

You can preview an EventBridge-shaped expression in Extended mode or generate one with Copy as. CronTool is not EventBridge's validator, so verify the six minute-first fields, required year, day-field ?, and cron(...) wrapper with AWS.

You can preview six- or seven-field expressions in Extended mode, but CronTool does not enforce Quartz's day-field ? rule. Verify required seconds, optional year, and special operators with Quartz.

Yes, preview Vercel's five-field schedule in Standard mode with timezone set to UTC. CronTool does not enforce plan limits: Hobby permits once per day, while Pro and Enterprise permit once per minute.

Not built-in, but the same parser CronTool uses (@datasert/cronjs-parser and @datasert/cronjs-matcher) is available on npm if you want to script tests in CI. Pair it with cronstrue for the natural-language description.

Include cron=<expression>, mode=extended when needed, and tz=<IANA zone> for timezone-sensitive runs. Copy link omits timezone.

Command execution is outside the test boundary. CronTool cannot inspect PATH, environment variables, permissions, logs, daemon state, or command success.