CRON expressions are powerful tools for scheduling tasks — from backups to emails — across servers, cloud platforms, and CI/CD pipelines. While they may look cryptic at first, once you decode the pattern, you unlock a whole new level of automation.
🔹 What is a CRON Expression?
A CRON expression is a string with 5 space-separated fields (sometimes 6 or 7 depending on the system) that define a recurring schedule.
┌──────── minute (0 - 59)
│ ┌────── hour (0 - 23)
│ │ ┌──── day of month (1 - 31)
│ │ │ ┌── month (1 - 12 or JAN-DEC)
│ │ │ │ ┌─ day of week (0 - 6 or SUN-SAT)
│ │ │ │ │
* * * * *🔹 Common Examples
| Expression | Meaning |
|---|---|
0 0 * * * | Every day at midnight |
*/5 * * * * | Every 5 minutes |
0 9 * * 1-5 | 9 AM on weekdays |
30 14 1 * * | 2:30 PM on the 1st of each month |
@daily | Shortcut for 0 0 * * * |
🔹 Special Characters
| Symbol | Meaning |
|---|---|
* | Every value |
, | List (e.g., MON,WED,FRI) |
- | Range (e.g., 1-5) |
/ | Step (e.g., */10 → every 10 units) |
🔹 Special Strings
| String | Equivalent CRON | Description |
|---|---|---|
@reboot | — | Run at system startup |
@yearly | 0 0 1 1 * | Once a year |
@monthly | 0 0 1 * * | Once a month |
@weekly | 0 0 * * 0 | Every Sunday |
@daily | 0 0 * * * | Every day at midnight |
@hourly | 0 * * * * | Every hour |
🔹 Tips & Tools
-
Always test your expressions using tools like crontab.guru or Cronhub.
-
This format changes based on the system. For example, the Quartz CRON scheduler has a slightly different format to support extra capabilities, such as seconds and nth recursive patterns, like the 3rd Friday of the month. Similarly AWS Cloudwatch has different one.