Cron expressions are the lingua franca of task scheduling — they power everything from nightly data pipelines to hourly reports to database maintenance jobs. But the syntax is notoriously cryptic, and a one-character error can shift a daily job to run once a month instead. A cron tester makes the timing visible before you deploy.
Cron Syntax: The Five (and Six) Fields
Standard 5-field cron: minute hour day-of-month month day-of-week. Each field accepts: a specific value (5), a range (1-5), a list (1,3,5), a step value (*/15 = every 15), or wildcard (*). Example: 0 9 * * 1-5 = "At 9:00 AM every weekday."
Many modern schedulers (AWS CloudWatch Events, Quartz, Kubernetes CronJobs) add a 6th field for seconds: second minute hour day-of-month month day-of-week. Some add a 7th for year. Always confirm which variant your platform uses — the defaults differ between systems.
Common Cron Patterns
*/5 * * * * — Every 5 minutes 0 * * * * — Every hour at the top of the hour 0 0 * * * — Daily at midnight 0 9 * * 1-5 — Weekdays at 9 AM 0 0 1 * * — First of every month at midnight 0 0 * * 0 — Every Sunday at midnight
The step value (*/n) is the most commonly misunderstood: */15 in the minute field doesn't mean "every 15 minutes starting from now" — it means "at minutes 0, 15, 30, 45 of every hour, unconditionally." This distinction matters if you're scheduling jobs relative to each other.
Timezone Gotchas in Cron Scheduling
Most cron systems default to UTC. If your job "runs at 9 AM" and your server is in UTC+5:30 (India), you need to set the cron to 3:30 AM UTC (09:00 - 05:30). Failing to account for timezone offsets is the #1 cause of "why is my report running at the wrong time" debugging sessions.
Daylight Saving Time (DST) adds complexity for any cron job targeting a local time. A job scheduled for 2:30 AM doesn't exist on the spring-forward night, and runs twice on the fall-back night. In UTC or timezones without DST (India Standard Time is fixed), this problem doesn't exist.
Never deploy a cron job without testing the expression first. What looks like "every 5 minutes" might actually be "never" or "once per hour" depending on a misplaced wildcard. The visualizer shows you the next 10 run times so there are no surprises in production.
Cron Builder — free, instant, no signup
100% client-side. Your data never leaves your browser.
Test Your Cron Expression →