Cron Expression Translator

If you've ever wondered what is a cron, here's the short version: cron is the scheduler that Unix and Linux systems use to run tasks automatically at set times. The name comes from chronos, Greek for time, and it has quietly powered the internet's routine work — backups, report emails, cache cleanups, health checks — for decades. The plain cron meaning is a clock-driven to-do list the machine works through on its own.

The thing cron runs is a cron job: a command or script paired with a schedule. The cron job meaning is exactly that pairing — "run this, on this cadence" — and the cadence is written as a cron expression. So the cron definition most people actually want is the expression itself: five fields that say when, and a command that says what. Get the five fields right and the job runs forever without anyone touching it; get them wrong and it either never fires or fires far more often than you meant.

A standard cron expression is five fields separated by spaces, always in the same order. Once you can read them left to right, the whole thing stops looking like line noise:

Each field understands four small operators, and every schedule you'll ever write is just a combination of them. A star (*) means every value — a star in the hour field is every hour. A comma makes a list, so 1,15,30 in the minute field fires three times an hour. A dash makes a range, so 1-5 in the day-of-week field is Monday through Friday. And a slash adds a step, so */15 is every fifteenth value and 0-30/10 is 0, 10, 20, 30.

Put together, these cover the common requests almost verbatim. A cron task every 5 minutes is */5 * * * *. A unix cron every 5 minutes during work hours is */5 9-17 * * 1-5. Crontab every 15 minutes is */15 * * * *, and a cron task every hour is 0 * * * *. The safest way to write one is to describe it in words first, then build the fields to match — which is exactly what the translator above lets you check in reverse.

Getting the expression right guarantees the scheduler will try to run your job on time. What it can't tell you is whether the job actually succeeded — or whether the thing it's supposed to keep healthy is still up. A cron job that fetches a health check runs perfectly and reports nothing when the site it checks has quietly gone down; the schedule fired, the work "happened," and no one is any wiser.

That's the gap between scheduling work and knowing it worked. Uptura sits on the second half: it runs the checks on a schedule for you — uptime, SSL, DNS, performance — confirms failures across consecutive runs so a blip doesn't page you, and actively tells you the moment something breaks, then again when it recovers. No crontab to maintain, no server to babysit, and alerts that reach you over email or Slack. Free during our public beta — so a scheduled job silently failing is something you hear about from us, not from a customer.