Developmentversion v1.0.0

Cron Expression Tool

Five fields, two questions: what does it mean, and when does it actually run. 0 0 13 * 5 is not Friday the 13th — it fires on the 13th and on every Friday, and this page says which rule produced every line it shows.

Expression● valid

every 15 minutes between 09:00 and 17:59, on Monday to Friday (UTC)

Day ruleday-of-month is *, so day-of-week alone decides the day.

Build it

minute*/15

hour9-17

day of month*

month*

day of week1-5

Zone

your zone · the CLI default is UTC

From

Next 5 runs

—

Privacy

Parsed and scheduled locally in your browser. Nothing you type is sent to the server.

The endpoint sends whatever you pipe it. Paste the five schedule fields, not the command that follows them: a crontab line carries the command, and commands carry passwords. This page makes no request while you use it — no logs, no analytics, no URL, no local storage.

The dialect

5-field POSIX cron, as Vixie and cronie implement it.

Five fields — minute, hour, day-of-month, month, day-of-week — plus the @ macros. A leading seconds field (Quartz, Spring) and Quartz’s ? L W # are refused rather than guessed at: Quartz numbers day-of-week 1–7 where POSIX uses 0–6, and guessing the engine means being wrong by a day.

Day-of-month and day-of-week combine with OR.

Whenever neither field’s text begins with *. The test is on the text, not the meaning, so */2 and 1-31/2 select the same sixteen days and schedule differently. Python’s croniter and several JS packages use the semantic rule instead; the line above always says which one produced this list.

Daylight saving follows cronie.

A job with * in the minute or hour field runs on the new time immediately: a repeated hour runs it twice, a skipped hour not at all. A fixed-time job runs once — at the transition instant if its time was skipped, at the first pass if its time happened twice. Note that cron uses the machine’s zone unless the crontab sets CRON_TZ=, while a Kubernetes CronJob runs in UTC unless .spec.timeZone is set.

From the command line

The expression goes in the body, because a query string truncates at # and a shell expands an unquoted * before curl ever sees it. The third command is a crontab linter: ?out=cron exits non-zero on bad syntax and on a schedule that never fires.

$printf '*/15 9-17 * * 1-5' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cron?tz=UTC&count=5'

$printf '*/15 9-17 * * 1-5' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cron?out=describe&tz=UTC'

$printf '*/15 9-17 * * 1-5' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cron?out=cron' >/dev/null || echo 'bad schedule'