Cron Expression Parser
Interpret traditional five-field cron expressions while surfacing day-field interaction, steps, dates, timezone, and dialect assumptions.
minute · hour · day of month · month · day of week
Try an expression
The schedule meaning, field expansion, warnings, and scope notes will appear here.
Reading Cron Correctly Means Reading Sets, Not Reading It Like a Sentence
Each cron field describes a set of matching values. 0,30 means two matching minutes. MON-FRI means a weekday range. */15means values reached by stepping through that field's full range from its first allowed value.
The daemon compares those sets with the current calendar time. The expression is not an interval timer counting fifteen minutes from whenever you installed it. That difference explains why a step in the hour field resets with the field range instead of remembering the previous process run.
10-30/5 Means “Step Through This Range,” Not “Every Five Minutes Forever”
In the minute field, 10-30/5 expands to 10, 15, 20, 25 and 30. The next hour starts the same rule again. */5 is different because its base is the complete minute range, so it matches 0, 5, 10 and so on.
Single-value step forms such as 5/10 are rejected in this portability-focused subset. If a particular scheduler documents an extension you rely on, validate it against that scheduler rather than assuming all cron implementations agree.
Day of Month and Day of Week Are the Part Most People Misread
In common Vixie/Cronie-style behavior, restricting both day fields does not turn them into an AND condition. A schedule such as 30 4 1,15 * FRI can run on the first and fifteenth of the month and on Fridays when the other fields match.
That expression may be syntactically perfect and still be wrong for someone who intended “Friday only when it is the first or fifteenth.” The parser flags the combination because this is a semantic mistake, not a syntax mistake.
Some Valid Field Values Can Describe an Impossible Calendar Date
Day 31 is allowed in the day-of-month field and February is allowed in the month field. Put them together and there is no date to match. A field-by-field syntax checker cannot discover that from range validation alone.
When month and day are simple explicit lists, Yoryantra performs a small cross-field check. February 29 remains possible because a five-field expression has no year field and leap years exist.
0 and 7 Both Mean Sunday in This Cron Family
Traditional crontab accepts Sunday as either 0 or 7. The parser treats those as the same semantic weekday when it expands a field, while preserving the original expression so you can see which form the author actually used.
The Expression Cannot Tell You Which Time Zone the Machine Uses
0 9 * * * says 09:00 according to the clock used by the scheduler. It does not contain “India,” “UTC,” or any other timezone. Cron implementations and surrounding platforms can add timezone configuration outside the five fields.
Daylight-saving transitions add another boundary: some local times can be skipped and others can occur twice. A parser can explain the field selection but cannot truthfully promise exact future run instants without knowing the target scheduler, timezone rules, and date range.
A Five-Field Cron Expression Is Not Automatically Portable to Every “Cron” Product
Quartz adds fields and tokens such as ?, L, W, and #. Cronie has extensions such as randomized ~ ranges. Cloud schedulers can have their own field counts and weekday rules.
A conservative traditional subset keeps a successful parse narrowly defined instead of implying that every cron-like scheduler accepts the same string.
Five Schedule Fields Are Not a Complete Crontab Entry
A user crontab line normally places the command after these five schedule fields. System crontabs such as /etc/crontaband files under /etc/cron.d also include a username before the command. Environment assignments such asCRON_TZ, SHELL, and PATH live outside the five-field expression as well.
Paste only the schedule portion here. A valid five-field parse does not validate the command, permissions, environment, working directory, or whether the target daemon has the same extensions.
The crontab Manual Is the Right Reference When a Field Rule Is Disputed
The Linux crontab(5) manual documents the five field ranges, names, lists, ranges, steps, Sunday numbering, day-field behavior, timezone handling, and Cronie-specific extensions. It is included here because those rules directly define the field rules described above.