Crontab Cheat Sheet & Builder

How to Use the Crontab Builder

1. Open the Builder tab — edit any of the five fields (minute, hour, day-of-month, month, day-of-week).
2. Watch the expression update — the full cron expression and its human-readable description update instantly as you type.
3. Use quick presets — click any preset button to populate the fields with a common schedule.
4. Browse examples — switch to the Examples tab and click any row to load it into the builder.
5. Copy the expression — click "Copy Expression" to copy the finished cron string to your clipboard.

Understanding Cron Expressions

A cron expression consists of five space-separated fields representing minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where Sunday is 0). Each field can contain a single value, a range (1-5), a list (1,3,5), a step value (*/15), or an asterisk (*) meaning "every valid value." Mastering these five fields lets you schedule virtually any recurring task — from simple daily backups to complex multi-conditional schedules.

Step Values — The Most Useful Pattern

The slash (/) character defines step values. The expression */5 in the minute field means "starting at 0, every 5 minutes" — so 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55. You can also write 10/5 to start at 10 instead of 0. Step values work in all five fields: */6 in the hour field means every 6 hours (midnight, 6am, noon, 6pm). This single feature covers the majority of real-world scheduling needs like health checks, cache warming, metrics aggregation, and report generation.

Ranges and Lists

Ranges (1-5) and lists (1,3,5) give you fine-grained control. The expression 0 9 * * 1-5 means 9:00 AM every weekday. The expression 0 9,13,17 * * 1-5 means 9 AM, 1 PM, and 5 PM on weekdays — useful for sending three digest emails per business day. You can combine ranges and lists: 1,3,5,7-9 in the hour field means hours 1, 3, 5, 7, 8, and 9. Mixing step values with ranges is also valid: 0-30/5 means every 5 minutes between the 0th and 30th minute of each hour.

Special Strings (@reboot, @daily, etc.)

Many cron implementations support shorthand strings as alternatives to the five-field format. @reboot runs once at system startup. @yearly (equivalent to 0 0 1 1 *) runs at midnight on January 1st. @monthly (0 0 1 * *) runs at midnight on the first of each month. @weekly (0 0 * * 0) runs at midnight on Sunday. @daily and @midnight both mean 0 0 * * *. @hourly means 0 * * * *. These aliases make crontabs easier to read at a glance, especially in shared server environments.

Debugging Cron Jobs

The most common mistake with cron is forgetting that the environment is minimal — cron runs with a restricted PATH and no shell aliases. Always use absolute paths in your cron commands (e.g., /usr/bin/python3 instead of python3). Redirect output to a log file to capture errors: * * * * * /path/to/script.sh >> /var/log/cron.log 2>&1. Check /var/log/syslog or /var/log/cron for execution records. Use crontab -l to list your current jobs and crontab -e to edit them. For complex schedules, always test with a more frequent expression first (like */5 * * * *) before setting the real schedule.

Cron vs. Systemd Timers vs. Cloud Schedulers

While cron is universal on Linux systems, modern alternatives offer more features. Systemd timers support calendar expressions, monotonic timers (run X minutes after last run), and restart-on-failure. AWS EventBridge, Google Cloud Scheduler, and Azure Logic Apps provide cloud-native scheduling with retry logic, monitoring, and dead-letter queues. GitHub Actions and GitLab CI support cron-syntax schedules for workflow automation. For high-reliability production jobs, consider pairing cron with a job monitoring service like Healthchecks.io, which pings your endpoint after each successful run and alerts you if a job is missed. See our Cron Parser to validate and explain any existing cron expression.