⏰ Cron Expression Builder & Explainer
Build and explain 5-field Unix cron expressions for Crontab, CI/CD pipelines, and task schedulers. Supports *, /, -, and , operators. Does not execute scheduled jobs — expression generation only.
Build and explain five-field Unix cron expressions using a visual interface. Set values for minute, hour, day of month, month, and day of week. Supports asterisk, step intervals, ranges, and list operators. Preset buttons cover common schedules like every hour and daily at midnight. Paste an expression to get a human-readable explanation. Does not schedule jobs.
What Is a Cron Builder?
This tool generates 5-field Unix cron expressions — the standard format used by Linux crontab, CI/CD pipeline schedulers, and Kubernetes CronJobs. You set values for five fields (minute, hour, day of month, month, and day of week), use preset buttons for common schedules, or paste an existing expression to get a human-readable explanation. The tool supports the standard operators: * (every), / (step interval), - (range), and , (list). All processing runs in your browser — this tool does not run, schedule, or monitor any jobs.
Cron Field Reference
| Field | Meaning | Typical Range | Operator |
|---|---|---|---|
| Minute | Minute of the hour | 0–59 | */15 = every 15 minutes |
| Hour | Hour of the day (24h) | 0–23 | 9-17 = 9 AM to 5 PM |
| Day of Month | Calendar day | 1–31 | 1,15 = 1st and 15th |
| Month | Month of year | 1–12 | */3 = every 3 months |
| Day of Week | Weekday (0=Sun, 7=Sun) | 0–7 | 1-5 = Monday–Friday |
Note: This tool uses 5-field POSIX cron syntax. Range validation is minimal — the fields accept free-text input. It does not support seconds (6-field), Quartz extensions (?, L, W, #), or named macros (@daily, @yearly).
Supported Operators
| Operator | Meaning | Example | Description |
|---|---|---|---|
* | Any value | * * * * * | Every minute of every day |
/ | Step interval | */5 * * * * | Every 5 minutes |
- | Range (inclusive) | 0 9-17 * * * | Every hour from 9 AM to 5 PM |
, | List of values | 0 9,13,17 * * * | At 9 AM, 1 PM, and 5 PM |
Common Cron Examples
| Expression | Schedule |
|---|---|
*/5 * * * * | Every 5 minutes |
0 * * * * | Every hour (at :00) |
0 0 * * * | Daily at midnight |
0 9 * * 1-5 | Weekdays at 9:00 AM |
0 0 1 * * | First day of every month |
*/30 * * * * | Every 30 minutes |
0 0 * * 0 | Weekly at midnight on Sunday |
When to Use This Builder
Developers, DevOps engineers, and system administrators use this tool to create and verify cron schedules for automated tasks:
- Linux crontab entries — build schedules for backup scripts, log rotation, and system maintenance tasks.
- CI/CD pipeline schedules — draft cron expressions for GitHub Actions, GitLab CI, Jenkins, and other scheduled workflows.
- Kubernetes CronJobs — construct the schedule field for K8s CronJob resources that run containers on a timer.
- Learning cron syntax — use the preset buttons and human-readable output to understand how cron fields and operators work.
- Decoding existing expressions — paste a cron expression into the explainer to get a plain-English breakdown of each field.
When NOT to rely on this tool: It does not execute, schedule, or monitor jobs. It does not calculate next-run timestamps. For timezone-aware scheduling or Quartz-compatible expressions, use a dedicated scheduler or framework library.
How It Works
The builder follows a straightforward pipeline, all running in your browser:
- Field input. You enter values for the five cron fields (minute, hour, day, month, weekday) or click a preset button to populate them automatically.
- Expression assembly. The five field values are joined with spaces to form a complete 5-field cron expression (e.g.,
0 9 * * 1-5). - Pattern matching. The assembled expression is checked against common preset patterns (daily at 9 AM, midnight, every N minutes, hourly). If it matches a known pattern, a friendly English description is shown.
- Fallback description. If the expression does not match a preset, a generic field-by-field description is generated — detailing what each field means.
- Display and copy. The cron expression and its description are displayed. You can copy the expression for use in crontab, CI/CD configs, or any cron-compatible scheduler. The optional explainer panel lets you paste an expression to decode it field-by-field.
How to Use the Cron Expression Builder
- Enter values for the five cron fields (minute, hour, day, month, weekday) or click a preset button like "Every 15m" or "Midnight."
- The 5-field cron expression and its human-readable description update instantly as you edit.
- Optionally paste an existing cron expression into the explainer to get a field-by-field breakdown.
- Copy the expression and use it in your crontab, CI/CD pipeline config, or any cron-compatible task scheduler.
Limitations
- Does not execute jobs. This tool generates cron expressions — it does not run, schedule, or monitor any tasks. The expression must be deployed to a cron daemon (crontab), CI/CD scheduler, or CronJob resource.
- 5-field Unix cron only. Seconds (6-field) and year (7-field) are not supported. Quartz-specific operators (
?,L,W,#) and named macros (@daily,@yearly) are not available. - No timezone support. Cron expressions are timezone-agnostic. The actual execution time depends on the timezone of the system running the cron daemon. There is no timezone selector or DST handling in this tool.
- No calendar validation. Invalid dates like February 31 or April 31 are accepted as-is. The tool joins field values without checking calendar logic.
- Minimal field validation. Fields accept free-text input — values outside typical ranges (e.g., minute=99) are not rejected. The explainer panel detects 5-field format errors but does not enforce range constraints.
- No next-run preview. The tool does not calculate upcoming execution times or timestamps.
- Platform differences. Day-of-month and day-of-week combinations are interpreted differently across cron implementations (some use OR logic, others AND). Test the expression in your target environment before deploying to production.
Privacy
Cron expressions are generated entirely in your browser. No expression data is sent to any server. No external cron API or scheduling service is used. ToolStand may record anonymized page-view and feature-interaction analytics (such as which preset was clicked), but the actual cron expressions you create are never collected or transmitted.
Frequently Asked Questions
What do the five cron fields mean?
A Unix cron expression has five space-separated fields: minute (0–59), hour (0–23), day of month (1–31), month (1–12), and day of week (0–7, where both 0 and 7 represent Sunday). The preset buttons and field labels in this tool show typical ranges — actual range validation is minimal.
Does this use Unix cron or Quartz cron?
Unix/POSIX cron (5-field). It does not support Quartz scheduler syntax. Quartz features such as ? (no-specific value), L (last), W (nearest weekday), # (nth weekday of month), and the optional seconds field are not available. If you need Quartz expressions, use a Quartz-specific cron generator.
Can I add seconds to the cron expression?
No. This tool generates 5-field expressions (minute hour day month weekday). Seconds are not supported. If your scheduler requires a 6-field format with seconds, you will need to prepend a seconds value manually or use a different tool.
Does the cron expression include a timezone?
No. Cron expressions are timezone-independent. The execution time depends on the system clock of the machine running the cron daemon. For example, 0 9 * * * will run at 9:00 AM in whatever timezone the server is configured with. This tool has no timezone selector and does not account for DST transitions.
Why can day-of-month and day-of-week behave differently?
In standard Unix cron, when both day-of-month and day-of-week are set to specific values (not *), the job runs when either condition matches — an OR relationship. However, some cron implementations (like certain cloud schedulers) use AND logic. Always verify behavior in your target environment.
Does this tool run the scheduled job for me?
No. This is an expression builder — it only generates and explains cron syntax. To actually execute a scheduled task, you must deploy the expression to a cron daemon (Linux crontab), a CI/CD pipeline scheduler, a Kubernetes CronJob, or a similar job-running system.