Cron Explainer

Translate cron expressions into plain English and validate the syntax

What is it and how does it work?

A cron explainer translates a cron expression — those terse strings like 0 9 * * 1 that schedule recurring jobs — into plain English you can actually read. Cron uses five fields (minute, hour, day of month, month, day of week) packed with numbers, asterisks and slashes, and the syntax is famously easy to misread. This tool decodes the expression into a sentence such as "At 09:00 on Monday", so you can confirm a schedule means what you intended before it goes live.

The reason this matters is that a small mistake in cron runs silently: a job set to fire at the wrong hour, every minute instead of once, or never at all because two fields conflict. By describing the schedule in words and validating the syntax, the explainer catches those errors at the moment you write them rather than days later when a report fails to send or a backup never runs. It works entirely in your browser, so you can check schedules for any server or pipeline privately.

Common use cases

• Verifying a new job: paste 0 9 * * 1 and confirm it reads "At 09:00 on Monday" before adding it to your crontab.
• Debugging a misfiring schedule: decode an existing expression to find why a job runs too often or at the wrong time.
• Learning cron syntax: try expressions and read the plain-English result to understand how the five fields combine.

Frequently asked questions

What do the five fields mean?

In order, they are minute, hour, day of month, month and day of week. An asterisk means "every" value for that field, so * * * * * runs every minute, while 0 9 * * 1 runs at 09:00 only on Mondays.

What does an asterisk or a slash do?

An asterisk (*) matches every value of a field. A slash defines a step: */15 in the minute field means "every 15 minutes". Combining them, like */5 9-17 * * *, schedules a job every 5 minutes between 9am and 5pm.

Why does my job run more often than expected?

Usually a field that should be specific was left as *. For example 0 * * * * runs every hour, not once a day, because the hour field is a wildcard. Reading the plain-English description makes this kind of slip obvious.

Does day of month and day of week together cause issues?

Yes — when both are set (not *), most cron implementations run the job if either matches, which can fire more often than intended. The explainer spells out the resulting schedule so you can see the combined effect.

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