Cron Expression Validator
Is this cron expression valid?
Checks the syntax, names the field that failed, and warns about the expressions that are valid but never fire — 30 February being the classic.
Questions people ask
The things that come up about cron expression validators, answered plainly.
Can a valid cron expression never run?
Yes. `0 0 30 2 *` is syntactically perfect and fires on 30 February, which does not exist. So is `0 0 31 4 *`. The validator checks for these rather than only checking the grammar.
Is @reboot a schedule?
No — it runs once when the daemon starts, so it has no next run to predict. The parser says so rather than failing silently.
Related tools
Julian days, Excel serials, GPS time, cron expressions and format validators.
Cron Expression ParserPaste an expression and get it back in English, field by field, with its next runs, how often it fires, and any trap it has walked into.
Cron Expression GeneratorPick a schedule and get the expression, described back to you in English and with its next five runs shown — so you can see what it does before it does it.
Cron Human Readable ConverterOne sentence describing what an expression does, plus a field-by-field breakdown — for putting in a comment, a runbook or a pull request description.
Timestamp ValidatorChecks a numeric timestamp for the mistakes that actually happen: the wrong unit, a 32-bit overflow, a sentinel value, or a date nowhere near where it should be.