Cron Expression Builder

A cron expression is a string of 5 fields (minute, hour, day-of-month, month, day-of-week) that define a schedule for recurring tasks. Format: * * * * * (minute hour day month weekday). For example, '0 9 * * 1-5' means 9:00 AM on weekdays. Most Linux systems, GitHub Actions, AWS EventBridge, and cron-based task runners support this format.

*/5 means 'every 5 units' — it starts at 0 and increments by 5 (0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55). 0,5,10,15,20,25,30,35,40,45,50,55 is the explicit equivalent. Both produce the same schedule. The step syntax (*/n) is cleaner for regular intervals; the list syntax is better for irregular intervals like 0,15,45.

Standard cron doesn't support 'last day of month' natively. Common workarounds: use 28 (safe for all months), or use a script that checks if tomorrow is the 1st. Some extended cron systems (like Quartz or node-cron) support L to mean last. AWS EventBridge supports L in day-of-month position.

System cron (Linux crontab) uses the server's local timezone, usually UTC in production. GitHub Actions uses UTC. AWS EventBridge uses UTC by default but supports timezone-aware schedules. Always specify timezones explicitly in your CI/CD config to avoid daylight saving time surprises. For Node.js cron jobs, use libraries like node-cron with the timezone option.

*/15 9-17 * * 1-5 — this runs every 15 minutes (at :00, :15, :30, :45) from 9:00 to 17:45 on Monday through Friday. Note: it runs at 17:00, 17:15, 17:30, 17:45 — within the 9-17 hour range. To stop at exactly 5pm, you'd need 0,15,30,45 9-16 * * 1-5 (runs from 9:00 to 16:45).