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Cron Expression Explainer

Read a five-field Unix cron expression and preview five upcoming times in a selected timezone. Calculations stay in this browser.

Minute · hour · day of month · month · day of week. Numbers, *, comma lists, ascending ranges, and */step or range/step only. Maximum 256 characters.

Defaults to your device clock. Occurrences must be strictly after this instant.

Ready. Set a reference and timezone, then explain the expression.

How to read five-field cron

minute hour day-of-month month day-of-week
  */15   *       *         *       *
FieldRange
Minute0–59
Hour0–23
Day of month1–31
Month1–12
Day of week0–7; Sunday is 0 or 7

Use * for all values, 1,3,5 for a list, 1-5 for a range, and */15 or 10-40/10 for a step. Selected values are expanded with the cron library.

Common cron examples

  • */15 * * * * — minute 0, 15, 30, and 45 of each hour.
  • 0 9 * * 1-5 — weekdays at 09:00 in the selected timezone.
  • 0 0 1 * * — midnight on the first day of each month.

When day-of-month and day-of-week are both restricted, this tool uses OR. For example, 0 9 1 * 1 matches 09:00 on the first day of a month or on Monday. If either day field is unrestricted, the other field controls the day match. Stepped or listed wildcards follow the library's semantics; expanded values and the day rule are shown together.

Frequently asked questions

Why are six-field expressions rejected?

This tool supports numeric Unix five-field cron only. Seconds, year fields, names, macros, Quartz modifiers, and alternative dialects are outside the supported subset.

Which timezone is used?

UTC is the default. Choose Asia/Jakarta or enter an IANA name supported by your browser. The reference must include Z or a UTC offset, so its meaning is independent of the device timezone.

What happens during daylight saving time?

Each occurrence includes its UTC instant and local offset. Frequent patterns continue through a repeated hour; a specific local time uses its first occurrence. Spring gap behavior is documented below using verified fixtures. Compare these estimates with your actual scheduler.

Will this run or save a job?

No. The tool calculates estimates locally; it does not schedule jobs or save input. Search is limited to five results before a maximum 40-year horizon, with a two-second worker timeout and explicit partial-result messages. Impossible dates can produce no occurrences.

Calculation policy

Results use the local browser distribution of Croner 10.0.2-dev.0, an upstream prerelease pinned to include its DST fall-back fix. This is a calculation preview and does not establish compatibility across cron dialects. Timezone data comes from the browser.

Verified spring-gap example for this pinned build: 30 2 * * * in America/New_York returns 03:30 at UTC-04:00 on 10 March 2024, then 02:30 the following day. The missing 02:30 shifts forward in this fixture. This differs from the upstream README's general statement that gap jobs are skipped; use the displayed instants and check your scheduler's policy.

Related developer tools

Inspect an occurrence with the Unix Timestamp Converter, read token time claims with the JWT Decoder, or browse Developer Tools.