Cron Expression Syntax: A Complete Guide with Examples

Cron is the original Unix job scheduler, and its expression syntax has become a cross-platform standard for describing recurring schedules in CI/CD pipelines, cloud functions, database maintenance windows, and task queues. The syntax is compact but easy to misread — a single character mistake can cause a job to run every minute instead of once a day.

The five standard fields

A standard cron expression has five space-separated fields:

┌─────────────── minute        (0–59)
│ ┌───────────── hour          (0–23)
│ │ ┌─────────── day of month  (1–31)
│ │ │ ┌───────── month         (1–12 or JAN–DEC)
│ │ │ │ ┌─────── day of week   (0–6, 0=Sunday, or SUN–SAT)
│ │ │ │ │
* * * * *

Field values and special characters

Common schedule patterns

Six-field cron (with seconds)

Some schedulers (Quartz, AWS EventBridge, GitHub Actions) add a sixth field for seconds or year. The order varies by platform:

# Quartz (seconds first)
0 0 12 * * ?        → every day at noon

# AWS EventBridge (seconds first, year last)
0 0 12 * * ? *      → every day at noon

Always check which variant your platform uses — mixing up the field order is a common source of confusion.

Special strings (vixie cron and systemd)

Many cron implementations support named shortcuts instead of numeric expressions:

• @yearly / @annually — equivalent to 0 0 1 1 *
• @monthly — equivalent to 0 0 1 * *
• @weekly — equivalent to 0 0 * * 0
• @daily / @midnight — equivalent to 0 0 * * *
• @hourly — equivalent to 0 * * * *
• @reboot — run once at startup (vixie cron only)

Platform differences to watch for

• Sunday is 0 or 7 — vixie cron accepts both 0 and 7 as Sunday; some platforms only accept 0.
• Day of month + day of week interaction — in most cron implementations, if both are non-*, the job runs when either condition is true (OR logic), not when both are true (AND). Quartz uses ? to say "don't care" for one of them.
• Timezone — cron traditionally runs in the server's local timezone. Cloud schedulers (AWS, GCP, GitHub Actions) let you specify a timezone explicitly — always do this for production jobs.
• GitHub Actions — uses UTC and the standard five-field format. Minimum interval is every 5 minutes.

Debugging tips

Before deploying a cron expression, run it through a parser that shows the next N execution times. A schedule that looks right in your head often has off-by-one errors in the day-of-week field (0 vs 7 for Sunday) or in step expressions (*/30 in the minute field runs at :00 and :30, not 30 minutes after the last run).