CRON Expression Builder
Edit each field or paste a full expression. Get a plain-English description instantly.
CRON Expression Builder
Cron Builder assembles a cron expression from five plain fields and explains in English what it will actually do, with presets for the common schedules.
How to use it
- Fill in the minute, hour, day of month, month, and day of week fields.
- Read the plain-English description of what it means.
- Use a preset for a common schedule, then adjust from there.
- Copy the finished expression.
The trap in the two day fields
Cron has five fields in order: minute, hour, day of month, month, day of week. An asterisk means every value, and a slash sets a step, so slash-five in the minute field means every five minutes.
The genuine trap is that day-of-month and day-of-week are combined with OR, not AND, whenever both are restricted. An expression asking for the 1st of the month and Monday does not mean the first Monday. It fires on the 1st and on every Monday. If you want the first Monday, cron cannot express it and you have to check the date inside your job.
Worked example
A common schedule:
- Expression0 9 * * 1-5
- Fieldsminute 0, hour 9, any day, any month, weekdays 1-5
Result: Nine o'clock every weekday morning.
When it helps
- Writing a schedule without looking up the field order again.
- Checking that an inherited cron line does what someone claims.
- Building a step or range expression correctly.
- Understanding why a job is firing more often than expected.
Common mistakes
- Restricting both day fields and expecting an AND. It is an OR, and this catches almost everyone once.
- Forgetting that cron runs in the server's timezone, which may not be yours and may not observe daylight saving the way you expect.
- Using both 0 and 7 for Sunday inconsistently. Most implementations accept either, which is fine until one does not.
