iLoveDevToolScenarios before syntax
Almost every scheduling need is one of six or seven shapes: poll every minute, clean up hourly, batch at midnight, report on Mondays, settle on the 1st, remind on weekday mornings. Copy the expression for your scenario first, understand the fields second — that's the fastest way to learn Cron.
The online Cron expression tool makes that the default flow: presets fill in with one click, the meaning shows as a plain sentence, and the next 5 run times appear right below.
High-frequency expressions by scenario
| Scenario | Expression | Notes |
|---|---|---|
| Every minute | * * * * * |
polling, health checks |
| Every 5 minutes | */5 * * * * |
step syntax, metrics collection |
| Hourly (at :00) | 0 * * * * |
minute 0, hour * |
| Daily at midnight | 0 0 * * * |
log rotation, batch jobs |
| Mondays at 9 | 0 9 * * 1 |
dow 1 = Monday (0 or 7 = Sunday) |
| 1st of the month | 0 0 1 * * |
settlement, billing |
| Weekdays at 8:30 | 30 8 * * 1-5 |
dow range = Mon–Fri |
The five fields, left to right: minute hour day-of-month month day-of-week, with ranges 0-59, 0-23, 1-31, 1-12, 0-7.
The three most common mistakes
- Hourly becomes every-minute:
* * * * *vs0 * * * *differ by one character and a world of meaning — the former runs every minute. Decide the minute field deliberately. - Day and weekday clash: in crontab, specifying both day-of-month and day-of-week is an OR, not an AND. "The 1st, but only if it's a Monday" needs conditional logic in your script — an expression alone can't express it.
- Missing the seconds field in Quartz: copying a 5-field Linux crontab into a Spring project fails — Quartz expects 6 fields starting with seconds.
Quartz vs crontab: know your scheduler
| Dimension | crontab | Quartz |
|---|---|---|
| Fields | 5 (min hour dom month dow) | 6 (sec + min hour dom month dow) |
| Granularity | minute | second |
? placeholder |
no | yes, for dom or dow |
| Ecosystem | Linux crontab command | Quartz / Spring @Scheduled |
Pick the format for your scheduler; don't let expressions cross ecosystems. The parser's format toggle flags pasted mismatches.
Verifying you got it right
The fastest check is the next 5 run times: paste into the Cron expression tool — if the list matches what's in your head, the expression is right; if not, compare against the plain-language meaning and the per-field breakdown. After deploy, confirm with the first execution in the logs, and convert for the server's timezone if it differs from yours.
Frequently Asked Questions
How do I write a Cron expression that runs every hour?
0 * * * * — minute field 0, hour field *. For the 30th minute of every hour, write 30 * * * *. Watch out: a * in the minute field means every minute, the single most common typo.
Can crontab and Quartz expressions be used interchangeably?
No. crontab is 5 fields (minute granularity); Quartz is 6 fields with a leading seconds position. Linux crontab won't accept 6 fields, and Quartz schedulers require the seconds field. Confirm your scheduler first, and switch the format toggle in a parser accordingly.
How can I verify an expression fires when I expect?
Paste it into an online parser and check the next 5 run times against your expectation — the fastest check. In production, confirm with the first execution in the logs; for cross-timezone servers, remember run times follow the server's timezone.