Cron Expressions¶

Detailed guide to cron expression syntax.

Format¶

┌───────────── minute (0-59)
│ ┌───────────── hour (0-23)
│ │ ┌───────────── day of month (1-31)
│ │ │ ┌───────────── month (1-12)
│ │ │ │ ┌───────────── day of week (0-6, Sun=0)
│ │ │ │ │
* * * * *

Field Values¶

Field	Values	Special Characters
Minute	0-59	`, - * /`
Hour	0-23	`, - * /`
Day of Month	1-31	`, - * / L W`
Month	1-12 or JAN-DEC	`, - * /`
Day of Week	0-6 or SUN-SAT	`, - * / L #`

Special Characters¶

Asterisk (*)¶

Match any value:

* * * * *     # Every minute
0 * * * *     # Every hour at minute 0

Comma (,)¶

List multiple values:

0 9,17 * * *  # 9 AM and 5 PM
0 0 1,15 * *  # 1st and 15th of month

Hyphen (-)¶

Range of values:

0 9-17 * * *  # Every hour 9 AM to 5 PM
0 0 * * 1-5   # Mon through Fri at midnight

Slash (/)¶

Step values:

*/15 * * * *  # Every 15 minutes
0 */2 * * *   # Every 2 hours

L (Last)¶

Last day:

0 0 L * *     # Last day of month
0 0 * * 5L    # Last Friday of month

W (Weekday)¶

Nearest weekday:

0 0 15W * *   # Nearest weekday to 15th
0 0 1W * *    # First weekday of month

Hash (#)¶

Nth occurrence:

0 0 * * 5#3   # Third Friday of month
0 0 * * 1#1   # First Monday of month

Examples¶

Time-Based¶

Cron	Description
`* * * * *`	Every minute
`/5 * * *`	Every 5 minutes
`0 * * * *`	Every hour
`0 /2 * *`	Every 2 hours
`0 0 * * *`	Daily at midnight
`0 9 * * *`	Daily at 9 AM
`0 9,18 * * *`	9 AM and 6 PM
`0 9-17 * * *`	Every hour 9 AM-5 PM
`30 9 * * *`	Daily at 9:30 AM

Day-Based¶

Cron	Description
`0 0 * * 0`	Every Sunday midnight
`0 9 * * 1`	Every Monday 9 AM
`0 9 * * 1-5`	Weekdays 9 AM
`0 9 * * 0,6`	Weekends 9 AM
`0 0 1 * *`	1st of month midnight
`0 0 1,15 * *`	1st and 15th
`0 0 L * *`	Last day of month

Month-Based¶

Cron	Description
`0 0 1 1 *`	January 1st
`0 0 1 /3 `	Every 3 months
`0 0 1 1,4,7,10 *`	Quarterly
`0 0 15 * *`	15th of each month

Complex¶

Cron	Description
`0 9 * * 1#1`	First Monday 9 AM
`0 9 * * 5L`	Last Friday 9 AM
`0 9 1W * *`	First weekday 9 AM
`0 0 1-7 * 1`	First Monday of month
`0 /4 * 1-5`	Every 4 hours weekdays

Business Scenarios¶

Daily Reports¶

# Daily at 9 AM
0 9 * * *

# Weekdays only at 9 AM
0 9 * * 1-5

Weekly Tasks¶

# Weekly Sunday maintenance
0 2 * * 0

# Weekly Monday standup reminder
0 8:55 * * 1

Monthly Tasks¶

# Monthly invoice on 1st
0 9 1 * *

# End of month report
0 17 L * *

Periodic Checks¶

# Health check every 5 minutes
*/5 * * * *

# Data sync every hour
0 * * * *

Validation¶

Check Syntax¶

m9m schedule validate "0 9 * * 1-5"

Preview Runs¶

m9m schedule preview "0 9 * * 1-5" --count 10

Output:

Next 10 runs:
1. Mon, 15 Jan 2024 09:00:00 UTC
2. Tue, 16 Jan 2024 09:00:00 UTC
3. Wed, 17 Jan 2024 09:00:00 UTC
...

Common Mistakes¶

Incorrect: Every Second¶

# WRONG - cron doesn't support seconds
* * * * * *

# RIGHT - minimum is every minute
* * * * *

Incorrect: Both Day Fields¶

Setting both day-of-month and day-of-week can be confusing:

# Runs on 15th AND every Monday (OR logic)
0 9 15 * 1

# For 15th only if it's Monday, use code logic

Incorrect: Step with Range¶

# WRONG
0 9-17/2 * * *

# RIGHT - step on full range
0 */2 * * *
# Or list specific hours
0 9,11,13,15,17 * * *

Online Tools¶

Test expressions before deploying:

crontab.guru - Visual cron editor
cronitor.io - Cron expression generator

Extended Syntax¶

Some systems support 6-field cron (with seconds):

┌───────────── second (0-59)
│ ┌───────────── minute (0-59)
│ │ ┌───────────── hour (0-23)
│ │ │ ┌───────────── day of month (1-31)
│ │ │ │ ┌───────────── month (1-12)
│ │ │ │ │ ┌───────────── day of week (0-6)
│ │ │ │ │ │
* * * * * *

m9m uses standard 5-field cron by default. Configure 6-field:

scheduling:
  cronFormat: "6-field"

Named Schedules¶

Use predefined names instead of expressions:

Name	Equivalent
`@yearly`	`0 0 1 1 *`
`@monthly`	`0 0 1 * *`
`@weekly`	`0 0 * * 0`
`@daily`	`0 0 * * *`
`@hourly`	`0 * * * *`

Example:

{
  "cronExpression": "@daily"
}