What is a cron expression and how does it work?

A cron expression is a string of five or six fields separated by spaces that defines a schedule for recurring tasks. The fields represent minute (0-59), hour (0-23), day of month (1-31), month (1-12), and day of week (0-6, where 0 is Sunday). Each field can contain specific values, ranges (1-5), lists (1,3,5), steps (*/5 for every 5 units), or wildcards (*). For example, '0 9 * * 1-5' means 'every weekday at 9:00 AM'. Our parser converts these cryptic expressions into human-readable descriptions and shows when the job will run next, making it easy to verify your schedule is correct before deploying.

How do I use the cron expression builder?

Click the 'Builder' tab to access the visual cron builder. You'll see five input fields representing minute, hour, day of month, month, and day of week. Enter values directly (use * for any, specific numbers, ranges like 1-5, or steps like */15), or click the preset buttons below for common schedules like 'Every hour', 'Weekdays at 09:00', or 'Monthly on 1st'. As you build, the tool shows a human-readable description and lists the next 5 run times. When satisfied, click 'Copy expression' to copy it, or 'Use in Parser' to test it in the parser tab. The builder includes helpful presets for hourly, daily, weekly, monthly, and quarterly schedules.

What cron expression formats are supported?

This tool supports standard 5-field cron expressions (minute, hour, day of month, month, day of week) compatible with Unix/Linux crontab, Kubernetes CronJobs, and most scheduling systems. You can use wildcards (*), specific values (0, 15), ranges (1-5), lists (1,3,5,7), and steps (*/5, 10-20/2). The parser handles complex expressions like '*/15 9-17 * * 1-5' (every 15 minutes during business hours on weekdays). While some systems support extended formats with seconds or year fields, this tool focuses on the widely-compatible 5-field format used by most Unix-like systems and modern orchestration platforms.

How do timezone settings affect cron schedule calculations?

Timezone is crucial for cron schedules because it determines when your job actually runs. When you parse an expression like '0 9 * * *' (daily at 9 AM), the tool calculates next run times in your selected timezone. By default, it uses your browser's detected timezone, but you can switch to UTC or other timezones using the timezone selector. This is especially important for distributed systems—if your server runs in UTC but you're thinking in EST, a job scheduled for '9 AM' will run at 9 AM UTC (4 AM EST). Always verify the next run times match your intended schedule. For production systems, explicitly specify timezone in your cron configuration to avoid surprises during daylight saving time changes.

What does the step syntax (*/5) mean in cron expressions?

The step syntax (*/5) means 'every 5th occurrence' in that time field. The asterisk (*) represents all possible values, and /5 means 'every 5th'. So */5 in the minute field means 'every 5 minutes' (0, 5, 10, 15... 55). In the hour field, */3 means 'every 3 hours' (0, 3, 6, 9, 12, 15, 18, 21). You can also apply steps to ranges: 10-30/5 in minutes means every 5 minutes between 10 and 30 (10, 15, 20, 25, 30). Common examples include */15 for every 15 minutes, */2 for every 2 hours, and */1 for every occurrence (equivalent to *). The builder includes preset buttons for popular step patterns like every 15 or 30 minutes.

Can I use ranges and lists together in cron expressions?

Yes! Cron expressions support combining ranges and lists for complex schedules. Use commas to separate multiple values or ranges. For example, '0 9,12,15 * * 1-5' runs at 9 AM, 12 PM, and 3 PM on weekdays. You can mix ranges like '1-5,10-15' for days 1-5 and 10-15 of the month. In the day of week field, '1-3,5' means Monday through Wednesday plus Friday. This flexibility lets you create sophisticated schedules without multiple cron jobs. However, remember that minute and hour use 0-based ranges (0-59 and 0-23), while day of month and month use 1-based ranges (1-31 and 1-12). Our parser validates these combinations and shows errors if values are out of range.

How do I schedule a job to run on the first day of every month?

Use '0 0 1 * *' to run at midnight on the 1st day of every month. Breaking it down: first 0 is minute 0, second 0 is hour 0 (midnight), 1 is day of month 1 (first day), and the two asterisks mean every month and every day of week. If you want a different time, adjust the hour and minute fields—for example, '0 9 1 * *' runs at 9 AM on the first of each month. For the first weekday (Monday-Friday) instead of just the 1st, you'd need additional logic outside cron. In the Builder tab, click the 'Monthly on 1st at 09:00' preset button to see this pattern in action. The parser shows the next 12 occurrences so you can verify it matches your schedule.

What's the difference between day of month and day of week fields?

Day of month (field 3) and day of week (field 5) specify when jobs run, but they combine with OR logic, not AND. Day of month is 1-31 for calendar dates (1st, 15th, 31st). Day of week is 0-6 where 0=Sunday, 1=Monday... 6=Saturday (some systems also accept 7 for Sunday). If you specify both, the job runs when EITHER condition is true. For example, '0 9 1 * 1' runs at 9 AM on the 1st of every month AND every Monday—not just Mondays that are the 1st. To run only on Mondays that are the 1st, use '0 9 1 * *' and add day-of-week logic in your script. For most schedules, set one to * (any) to avoid confusion. Use '* * * * 1-5' for weekdays or '* * 1 * *' for monthly, but not both together.

Can I validate my cron expression before deploying it?

Absolutely! That's the primary purpose of this tool. Paste your cron expression into the Parser tab, and it instantly shows a human-readable description like 'Every 5 minutes' or 'At 09:00 AM, Monday through Friday'. Below that, it lists the next 5 (or custom count) run times in your selected timezone. If the expression is invalid—wrong syntax, out-of-range values, or malformed fields—you'll see an error message explaining the issue. This real-time validation catches mistakes like using 60 for minutes (max is 59) or 32 for day of month (max is 31). Always verify the next run times match your expectations, especially for timezone-sensitive schedules or complex expressions with ranges and steps. Testing in the parser prevents production surprises.

How do I create a cron expression for business hours only?

To run during business hours (9 AM to 5 PM, weekdays only), use hour ranges and day of week ranges. For example, '0 9-17 * * 1-5' runs every hour from 9 AM to 5 PM, Monday through Friday. If you want every 30 minutes during business hours, use '*/30 9-17 * * 1-5'. For finer control, specify exact hours: '0 9,10,11,12,13,14,15,16,17 * * 1-5' (every hour on the hour during business hours). Remember that hour 17 is 5 PM, and the job runs at the start of that hour. If you want to stop at 4:30 PM instead of 5 PM, use '*/30 9-16 * * 1-5'. The Builder tab includes a 'Weekdays at 09:00' preset you can customize. Always check the next run times to verify the schedule matches your business hours and timezone.

Free Cron Expression Parser & Builder

Parse and build cron expressions with human-readable descriptions and next run times. Visual builder with timezone support and common presets for easy scheduling. Perfect for developers, DevOps, and system administrators.

Cron Tools

Parse, build, and understand cron expressions

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Cron Parser FAQ - Common Questions

Find answers to frequently asked questions about cron expressions, cron syntax, scheduling tasks, timezone handling, and using our free cron parser and builder tool.

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