What is the format of a cron expression?

A standard cron expression has five space-separated fields: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where both 0 and 7 mean Sunday). Each field accepts a number, a wildcard (*), a range (1-5), a list (1,3,5), or a step (*/5).

What does */5 mean in a cron field?

"*/5" means "every 5 units." In the minute field it means every 5 minutes (0, 5, 10, …, 55). In the hour field it means every 5 hours. The step syntax works in any field.

Does this support @reboot or @daily shorthand?

Yes — common @ shortcuts such as @reboot, @yearly, @annually, @monthly, @weekly, @daily, @midnight, and @hourly are recognized and explained.

Are the next run times in UTC or local time?

The next run times are shown in your browser's local timezone since the calculation happens entirely in JavaScript on your device.

Why does day-of-month AND day-of-week both restrict the schedule?

In standard cron, if both day-of-month and day-of-week are not wildcards, cron fires when EITHER condition is true (union, not intersection). This is a common source of confusion.

Crontab Syntax Validator

Name: Crontab Syntax Validator
Availability: InStock
Author: Nham Vu

Paste a cron expression to instantly validate its syntax and get a plain-English explanation of when it runs.

Cron Expression

Minute

Hour

Day

Month

Weekday

Common Presets

Plain-English Summary

Enter a cron expression on the left to see its explanation here.

Next 5 Run Times (local time)

Waiting for a valid expression…

Summary

Paste a cron expression to instantly validate its syntax and get a plain-English explanation of when it runs.

How it works

Type or paste your cron expression (5 fields separated by spaces) into the input box.
The validator checks each field for correct syntax as you type.
Each field is highlighted with a color-coded explanation.
The tool computes the next 5 run times based on the current local time.
Common presets let you quickly insert standard schedules like "every hour" or "daily at midnight".

Use cases

Debug a crontab entry that is not firing at the expected time.
Learn what an unfamiliar cron expression means at a glance.
Verify a new schedule before adding it to a production server.
Cross-check cron expressions generated by third-party tools or AI.
Quickly insert common schedules using the preset buttons.
Preview the exact next run times to avoid unintended overlap.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu