Cron Expression Syntax Guide
Write and debug cron schedule expressions for task automation, with examples for common scheduling patterns.
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Cron Expression Syntax
Cron expressions define recurring schedules using five fields: minute, hour, day of month, month, and day of week. Mastering this syntax lets you schedule tasks with precision.
The Five Fields
┌───── minute (0-59)
│ ┌───── hour (0-23)
│ │ ┌───── day of month (1-31)
│ │ │ ┌───── month (1-12)
│ │ │ │ ┌───── day of week (0-7, both 0 and 7 = Sunday)
* * * * *
An asterisk means "every value." A specific number means "only at that value." Ranges (1-5), lists (1,3,5), and step values (*/5 = every 5th) provide additional precision.
Common Patterns
0 9 * * 1-5 — 9:00 AM every weekday. */15 * * * * — every 15 minutes. 0 0 1 * * — midnight on the first of every month. 30 2 * * 0 — 2:30 AM every Sunday. 0 */6 * * * — every 6 hours (midnight, 6am, noon, 6pm).
Timezone Considerations
Cron traditionally runs in the server's timezone. If your server is in UTC and you want a job at 9 AM Eastern, you need to account for the offset — and the offset changes with daylight saving time (UTC-5 in winter, UTC-4 in summer). Modern cron implementations support CRON_TZ or the TZ directive to specify the intended timezone.
Testing Expressions
Browser-based cron expression tools show the next N execution times for any expression. Enter your cron expression and verify that the scheduled times match your intent. Pay special attention to edge cases: the 31st of months that have 30 days, February 29th, and timezone transitions.
Common Mistakes
0 0 * * 7 runs on Sunday (both 0 and 7 mean Sunday in most implementations). 0 0 31 * * only fires in months with 31 days. */10 9-17 * * * fires every 10 minutes during business hours, but includes 17:00, 17:10, etc. if you meant "until 5 PM", use 9-16. Step values start from 0: */3 in the hour field means 0, 3, 6, 9... not 1, 4, 7, 10.
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