What is a cron expression?

A cron expression is a string of five space-separated fields that represent a schedule. The fields are: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6). For example, '0 9 * * 1-5' means 9:00 AM every weekday.

How do I validate a cron expression?

Enter your cron expression in the input field on CronTab.space. The validator instantly checks the syntax and shows any errors. Valid expressions display a human-readable description and the next 5 scheduled execution times.

What does the asterisk (*) mean in cron?

The asterisk (*) in a cron expression means 'every' or 'any value'. For example, * in the minute field means every minute, and * in the day field means every day of the month.

How do I schedule a cron job to run every 5 minutes?

To run a cron job every 5 minutes, use the expression '*/5 * * * *'. The */5 in the minute field means every 5th minute, and the asterisks in other fields mean any hour, day, month, and weekday.

Can I generate a cron expression using natural language?

Yes! CronTab.space features an AI-powered generator. Simply type your schedule in plain English like 'every Monday at 9am' or 'twice daily' and the AI will generate the correct cron expression for you.

crontab.space/cron / 0 0 L 3,6,9,12 *

0 0 L 3,6,9,12 *

At 12:00 AM, on the last day of the month, only in March, June, September, and December

open in builder →

next: Tue, Jun 30, 12:00 AM UTC

At a glance

meansat 12:00 am, on the last day of the month, only in march, june, september, and december

frequencyoccasional

next runTue, Jun 30, 12:00 AM UTC

syntaxstandard 5-field cron

See it on a calendar

UTC · no runs in window

036912151821Mon

Tue

Wed

Thu

Fri

Sat

Sun

less

Next runs

Tue, Jun 30, 12:00 AM UTC

Wed, Sep 30, 12:00 AM UTC

Thu, Dec 31, 12:00 AM UTC

Wed, Mar 31, 12:00 AM UTC

Wed, Jun 30, 12:00 AM UTC

Thu, Sep 30, 12:00 AM UTC

Use it in

# /etc/crontab
0 0 L 3,6,9,12 *  user  /usr/local/bin/your-script.sh

Snippets are templates — replace placeholders with your script and paths.

Going to production? Cron won’t tell you when it fails.

Standard cron silently skips runs when the machine is off, the script crashes, or the network drops. Get an alert the moment a scheduled run misses its window.

Monitor with cronradar

Field by field

min

hour

dom

mon

3,6,9,12

dow

any

minute · hour · day of month · month · day of week

Variations

0 0 L * *

Last day of the month at midnight

0 0 * * *

Every day at midnight

0 0 1 * *

Midnight on the 1st of every month

0 0 15 * *

15th of the month at midnight

What does 0 0 L 3,6,9,12 * mean?

The cron expression 0 0 L 3,6,9,12 * runs at 12:00 am, on the last day of the month, only in march, june, september, and december. Cron expressions have five fields — minute, hour, day of month, month, and day of week — separated by spaces. Each field controls one piece of the schedule.

When you’d use this

This schedule is a common fit for jobs that need to run at midnight — log rotation, backups, daily cleanup. Paste it into your crontab, a node-cron call, a Kubernetes CronJob manifest, or a GitHub Actions workflow — the snippets above are ready to copy.

Gotchas

Cron runs in the system’s timezone unless you set TZ or schedule in UTC. Missed runs are not retroactively executed by standard cron — use anacron or systemd timers with Persistent=true if you need catch-up. Day-of-month and day-of-week combine with OR semantics in most cron implementations, which can be surprising.

FAQ

An asterisk matches every valid value for that field. In the minute field it means every minute; in the hour field, every hour, and so on. "* * * * *" runs every minute of every hour, every day.

Both. Standard cron accepts 0 and 7 as Sunday. Day-of-week runs Sunday=0, Monday=1, ..., Saturday=6, with 7 also recognized for Sunday in most implementations.

No. Standard cron only fires at the exact scheduled times — there is no catch-up. If you need missed-run recovery, look at anacron, systemd timers with Persistent=true, or a job scheduler like Quartz.

Quartz uses 6- or 7-field expressions with seconds and optional year, plus extras like "L" (last) and "#" (nth weekday). Standard Unix cron is 5 fields: minute, hour, day-of-month, month, day-of-week.

Cron runs in the timezone of the system or the configured TZ. During DST transitions, a missing hour is skipped and a repeated hour fires twice. Use UTC scheduling for predictable behavior across regions.