Cron Builder
Describe each cron field with ranges, steps and lists, then preview the next run times.
Describe each field, then preview the next runs
How to use Cron Builder
Cron Builder turns a schedule you can describe in words into a standard 5-field cron expression, and shows the next five run times so you can verify it before pasting it anywhere.
Open Cron Builder on toolpermarket and enter your values in the fields below.
In the Each field mode field, for Minute, Hour, Day of month, Month and Day of week, pick Every, a specific value, a list, a range or a step. a step such as */15 means "every 15" of that unit.
In the Field value field, type the value, list, range or step number the mode needs. leave it blank for Every, which becomes an asterisk.
In the Preview field, press Build & preview to see the expression and the next runs. the preview uses the server clock, so compare it with your own timezone.
Press Build & preview to compute the result. The output appears immediately below the form. You can change any input and run it again to compare results.
Read the result and use it as needed. If the number looks off, re-check your inputs and run it again — the math is deterministic, so the same entries always return the same answer.
Worked example. Set Minute to step 15, Hour to Every, and the rest to Every to get "*/15 * * * *" — a job that runs every 15 minutes.
Tips for accurate results.
Use a range like 1-5 for Day of week to target Monday through Friday only.
Pin both Minute and Hour to fixed values if you want the job to run once, not every minute of an hour.
When you restrict both day-of-month and day-of-week, the two are treated as "either", so a date OR a weekday will trigger it.
When to use Cron Builder. Scheduling a backup, report or cache clear that should run at the same time each day. Building the schedule string before pasting it into crontab, CI or a container scheduler. Double-checking that a hand-written expression actually fires when you expect.
When you actually reach for this
- You need a cron expression and do not want to memorise the five-field order.
- You want to sanity-check when a schedule will actually fire before deploying it.
Where this tool stops being accurate
- It builds standard five-field expressions; Quartz and some platforms use extra fields.
- The preview uses the server clock, so compare it with the timezone your scheduler runs in.
- When both day-of-month and day-of-week are restricted they are OR-ed, which surprises most people.
Frequently asked questions
What do the five fields mean?
They are minute, hour, day-of-month, month and day-of-week, in that order. An asterisk means "every" value for that field.
What does a step like */15 do?
It runs every 15 units of that field — so in the minute field it fires at :00, :15, :30 and :45. In the hour field it would fire every 15 hours.
Why does my next-run preview show nothing?
Usually the combination can never occur, such as day 31 in a 30-day month, or a range that excludes all valid dates. Adjust the fields and preview again.
How do I run only on weekdays?
Set Day of week to a range 1-5 and leave Day of month as Every. Because both are restricted otherwise they are OR-ed, keeping Day of month as Every avoids that.
Does this connect to a scheduler?
No. It only builds and previews the expression. You copy the result into your own cron daemon or CI configuration.
Will the same expression work in GitHub Actions?
GitHub Actions uses POSIX cron but runs in UTC and treats day-of-month and day-of-week with OR semantics, so re-check both the dialect and the timezone before relying on it.