Cron expression explainer

Read a cron expression in plain English

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How it works

A cron expression sets when a job runs, using five fields: minute, hour, day of the month, month and day of the week. A star means every value. So 0 9 * * 1-5 means 09:00 on weekdays. Paste one to read it in plain English and see its next five runs in your own time.

minute hour day of month month day of week

We check each field, and name exactly what’s wrong if one isn’t valid. If you set both a day of the month and a day of the week, standard cron runs on either one.

Worked example. 0 9 * * 1-5 means minute 0, hour 9, any day, any month, Monday to Friday: At 09:00 on Monday, Tuesday, Wednesday, Thursday and Friday.

Examples

Expression	Meaning
/5 * * *	Every 5 minutes
0 * * * *	At the start of every hour
0 0 * * *	At 00:00
0 9 * * 1-5	At 09:00 on Monday, Tuesday, Wednesday, Thursday and Friday
0 0 1 * *	At 00:00 on day 1 of the month

What this tool doesn’t cover

Some systems add their own symbols, such as ? and L, which this doesn’t read.
Next runs use your own time zone, and your server may use another.

Questions

What does */5 mean?

Every 5 units. In the minute field, that’s every 5 minutes.

Is Sunday 0 or 7?

Both work.

What time zone does cron use?

Usually the server’s. Check yours, because next runs here use your own zone.

How do I read a cron expression?

The five fields are minute, hour, day of the month, month and day of the week. A * means every value.

How do I run a job every day at midnight?

Use 0 0 * * *. That means minute 0 of hour 0, on every day.

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Sources: POSIX crontab (opens in a new tab)