Cron Expression Tester — Validate and Understand Cron Jobs in Your Browser
Test and validate cron expressions instantly. See the next run times, understand the schedule, and debug cron syntax — all in your browser with no data sent anywhere.
Cron expressions are powerful but easy to get wrong. A single misplaced character can mean a job runs every minute instead of every day, or not at all. SimpleTools Cron Tester lets you validate cron expressions instantly and see exactly when they’ll trigger — all in your browser.
What Is a Cron Expression?
Cron is a time-based job scheduler in Unix-like operating systems. A cron expression is a string of five (or six) fields that define a schedule:
┌───────────── minute (0–59)
│ ┌───────────── hour (0–23)
│ │ ┌───────────── day of month (1–31)
│ │ │ ┌───────────── month (1–12 or JAN–DEC)
│ │ │ │ ┌───────────── day of week (0–6 or SUN–SAT)
│ │ │ │ │
* * * * *Common examples:
| Expression | Meaning |
|---|---|
* * * * * | Every minute |
0 * * * * | Every hour, on the hour |
0 9 * * 1-5 | Every weekday at 9:00 AM |
0 0 1 * * | At midnight on the 1st of every month |
*/15 * * * * | Every 15 minutes |
0 2 * * 0 | Every Sunday at 2:00 AM |
Why Test Cron Expressions?
Getting cron expressions right is harder than it looks:
- Timezone confusion — cron runs in the server’s timezone, not yours
- Off-by-one errors — does
0 9 * * 0mean Sunday or Monday? - Overlapping schedules — a job scheduled to run hourly may overlap if it takes over an hour
- Complex expressions — step values (
*/5), ranges (1-5), and lists (1,3,5) can combine in confusing ways
Debugging a broken cron expression in production means waiting hours or days to observe the actual run behaviour. With SimpleTools Cron Tester, you see the next 10 (or 50) run times instantly.
How It Works
The tool uses a cron parsing library running entirely in JavaScript in your browser. When you enter an expression:
- The parser validates the syntax and highlights any errors
- A human-readable description is generated (e.g., “At 9:00 AM, Monday through Friday”)
- The next N run times are computed from the current moment (or a custom start time)
- Results are displayed in your local timezone or UTC — your choice
No server, no API, no round-trip. All computation happens in your browser tab.
How to Use the Cron Tester
- Go to simpletools.one/cron-tester
- Type or paste your cron expression into the input field
- See the human-readable description appear instantly
- View the list of upcoming scheduled run times
- Adjust the timezone if needed to match your server environment
- Use the Common Expressions quick-select for frequently-used schedules
Common Cron Mistakes and How to Spot Them
Mistake: * * * * 1 — thinking this means “every Monday” Reality: It means “every minute of every hour on every day in every month, on Mondays only” — so yes, it does run only on Mondays, but every minute of those days.
Mistake: 0 9-17 * * 1-5 — intending “every hour from 9–17 on weekdays” Reality: This is actually correct! It runs at minute 0 of hours 9 through 17.
Mistake: 30 9 * * * expecting local time Reality: The server may be in UTC; 9:30 UTC could be 4:30 AM your time. Always verify timezone.
Cron Syntax Extensions
The tester also supports extended cron syntax used by systems like AWS EventBridge, GitHub Actions, and Kubernetes CronJobs:
- 6-field cron (with seconds):
*/30 * * * * *— every 30 seconds - Special strings:
@hourly,@daily,@weekly,@monthly,@yearly,@reboot ?wildcard in day-of-month or day-of-week (Quartz-style)
Who Is This For?
- DevOps engineers scheduling jobs in Kubernetes, AWS Lambda, or Linux crontabs
- Developers setting up recurring tasks in cloud schedulers
- Database administrators scheduling backups and maintenance windows
- Anyone who’s ever stared at a cron expression and wondered “when exactly does this run?”
Test your cron expressions now at simpletools.one/cron-tester — instant, accurate, and completely private.