Cron Expression Generator
Build, validate, and understand cron expressions visually. Get a human-readable description and see the next 10 scheduled run times.
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Common Schedules:
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What Is a Cron Job?
A cron job is a time-based task scheduler in Unix-like operating systems (Linux, macOS, BSD). It allows you to schedule commands or scripts to run automatically at specific intervals — every minute, every hour, once a day, on the first Monday of each month, or any other combination. The name "cron" comes from the Greek word "chronos" (time). Cron is one of the oldest and most reliable scheduling systems in computing, running continuously as a background daemon since its creation in the 1970s.
Cron jobs are essential for system administration and application maintenance. They handle tasks that need to run regularly without human intervention: database backups, log rotation, email reports, cache clearing, certificate renewal, and data synchronisation.
Cron Expression Format
A cron expression consists of 5 fields separated by spaces: minute hour day-of-month month day-of-week
| Field | Range | Special Characters | Example |
|---|---|---|---|
| Minute | 0–59 | * , - / | */15 = every 15 minutes |
| Hour | 0–23 | * , - / | 9-17 = business hours |
| Day of Month | 1–31 | * , - / | 1,15 = 1st and 15th |
| Month | 1–12 | * , - / | 1-6 = January to June |
| Day of Week | 0–6 (Sun=0) | * , - / | 1-5 = weekdays only |
Special Characters Explained
*(wildcard): Matches every value in the field.* * * * *runs every minute of every hour of every day.,(list): Specifies multiple values.1,3,5in the day-of-week field means Monday, Wednesday, Friday.-(range): Specifies a range.9-17in the hour field means every hour from 9 AM to 5 PM./(step): Specifies intervals.*/5in the minute field means every 5 minutes.0-30/10means 0, 10, 20, 30.
Special Shortcut Strings
Some cron implementations (including most Linux distributions) support convenient shortcut strings:
@yearly/@annually— equivalent to0 0 1 1 *(midnight, January 1)@monthly— equivalent to0 0 1 * *(midnight, first day of every month)@weekly— equivalent to0 0 * * 0(midnight every Sunday)@daily/@midnight— equivalent to0 0 * * *(midnight every day)@hourly— equivalent to0 * * * *(start of every hour)@reboot— runs once at system startup (not time-based)
Real-World Cron Job Examples
| Expression | Schedule | Use Case |
|---|---|---|
0 2 * * * | Daily at 2:00 AM | Database backup during low-traffic hours |
0 9 * * 1 | Every Monday at 9:00 AM | Send weekly analytics report email |
*/30 * * * * | Every 30 minutes | Health check / disk space monitoring |
0 3 * * 0 | Every Sunday at 3:00 AM | Clear temporary files and logs |
0 8 1 * * | 1st of each month at 8:00 AM | Generate monthly invoices |
0 0 * * 1-5 | Midnight, weekdays only | Sync data from external API on business days |
0 */6 * * * | Every 6 hours | Renew SSL certificates (Let's Encrypt check) |
*/5 9-17 * * 1-5 | Every 5 min, 9AM–5PM, Mon–Fri | Check for new orders during business hours |
Cron vs Other Schedulers
- Cron (Linux/macOS): Built-in, reliable, no dependencies. Edit with
crontab -e. Best for server-side tasks on Unix systems. - Systemd Timers (Linux): Modern alternative to cron on systemd-based Linux. Offers better logging, dependency management, and resource control. More complex to set up.
- Windows Task Scheduler: The Windows equivalent of cron. Uses a GUI or
schtaskscommand. Supports triggers beyond time (login, event, idle). - Cloud Schedulers: AWS EventBridge (CloudWatch Events), Google Cloud Scheduler, and Azure Logic Apps provide cron-like scheduling for cloud functions and serverless architectures.
Best Practices
- Log output: Always redirect output to a log file:
0 2 * * * /path/to/script.sh >> /var/log/backup.log 2>&1 - Use absolute paths: Cron runs with a minimal environment. Always use full paths for commands and files.
- Avoid overlapping runs: If a job takes longer than the interval, use a lock file (flock) to prevent multiple instances.
- Set the PATH: Add
PATH=/usr/local/bin:/usr/bin:/binat the top of your crontab to ensure commands are found. - Test manually first: Run the command by hand before scheduling it. Cron will not show errors unless you capture them.
Frequently Asked Questions — Cron Expression Generator
A cron expression is a string of 5 fields that define a schedule: minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-7, where 0 and 7 are Sunday). Special characters: * (any), , (list), - (range), / (step). Example: "0 9 * * 1" means "at 9:00 AM every Monday." Cron runs on Unix/Linux systems and cloud schedulers to automate recurring tasks.
* means "every" (any value). , separates multiple values (1,3,5 = 1st, 3rd, 5th). - defines a range (1-5 = 1 through 5). / defines steps (*/15 = every 15 units, 0-30/10 = 0, 10, 20, 30). Examples: "*/5 * * * *" = every 5 minutes; "0 9-17 * * 1-5" = every hour from 9 AM to 5 PM on weekdays; "0 0 1,15 * *" = midnight on the 1st and 15th of each month.
Frequently used cron expressions: @yearly / 0 0 1 1 * (once a year, Jan 1 midnight), @monthly / 0 0 1 * * (once a month, 1st at midnight), @weekly / 0 0 * * 0 (every Sunday at midnight), @daily / 0 0 * * * (every day at midnight), @hourly / 0 * * * * (every hour), */5 * * * * (every 5 minutes), 0 */6 * * * (every 6 hours).
Traditional cron (Unix crontab) has minute-level precision — the smallest interval is 1 minute. For sub-minute scheduling, use tools like Quartz Scheduler (Java, supports seconds as a 6th field), AWS EventBridge (1-minute minimum), or application-level job schedulers. Some systems add a seconds field as the first position, making it a 6-field expression.
Common issues: (1) Timezone — cron runs in the server's local timezone; always verify or set TZ explicitly. (2) Day-of-month vs day-of-week — when both are specified (not *), most systems run if either matches (OR logic, not AND). (3) Daylight saving — "0 2 * * *" may never run or run twice during DST transitions. (4) System clock drift. (5) The cron daemon isn't running or the job file has syntax errors.