Your cron expression can be valid and still never run

A cron parser can answer one question—does this have five fields and legal tokens?—while your scheduler needs a different answer: will this job ever run, and will it run when I intended?

That gap is where silent cron failures live. A schedule can be syntactically valid, return no parser error, and still be impossible, surprisingly broad, or operationally noisy. Here is a small semantic checklist you can run before deploying a schedule.

1. Check the calendar, not only the grammar

Consider:

Your cron expression can be valid and still never run

Related reading

Reading cron expressions

Cron expressions are hard to verify — so I built `croncheck`

Stop googling cron syntax. Read it in plain English instead

I finally understood cron expressions by building an explainer for them

Cron Expressions, LLMs, and Investigating Crimes You Committed

Cron Expressions: a Cron Expressions tool that never sees your data