Cron Expression Explainer

Common cron expressions in plain English

The five fields of a cron expression

Cron syntax: star, comma, dash and slash

Cron macros: @daily, @hourly and the rest

Day of month and day of week together

How to read a cron expression

1. Paste the expression. Type or paste five fields separated by spaces, such as */15 9-17 * * MON-FRI, or a macro such as @daily.
2. Read the description. The sentence under the box says when the job runs. Below it, a table reads each field on its own, so you can see which part means what.
3. Fix any error. If a field is wrong, the message names it and says what is allowed there: for example, that the minute must be 0–59 or that a range cannot run backwards.
4. Check the next run times. The list shows the next 10 times the job runs, starting from now. Switch between your own time zone and UTC to see them as a server set to UTC would run them.

Frequently asked questions

What do the five fields of a cron expression mean?

From left to right: minute (0–59), hour (0–23), day of month (1–31), month (1–12 or JAN–DEC) and day of week (0–7 or SUN–SAT, where 0 and 7 are both Sunday). A star means every value. For example, */15 9-17 * * MON-FRI reads as: Every 15 minutes, between 09:00 and 17:59, on Monday through Friday.

What happens when both day of month and day of week are set?

The job runs when either one matches, not only when both do. This is the POSIX rule, and Vixie cron and cronie follow it. At 00:00, on the 13th of the month, or on Friday: so 0 0 13 * FRI runs on every 13th and on every Friday, not just Friday the 13th. To run only when both match, leave one of the two as a star and test the other condition inside the job (for example, check the weekday in the script).

Why does */2 in the day-of-month field behave differently?

Vixie cron and cronie treat a day field as unrestricted when its text starts with a star, even with a step. So 0 0 */2 * MON counts day of month as unrestricted and requires both to match: every second day of the month that is also a Monday. This tool follows that behavior and labels the result so you can see it. The POSIX text only talks about fields given as an element or list, so other cron implementations may differ here.

Is 7 Sunday in cron?

Yes. Day of week runs from 0 to 6 with 0 as Sunday, and most crons also accept 7 as Sunday, so 5-7 means Friday through Sunday. The names SUN to SAT work too. A range cannot wrap around, so FRI-MON is an error: write FRI,SAT,SUN,MON or 5-7,1.

What do @daily, @hourly and the other macros mean?

@yearly (or @annually) is 0 0 1 1 *, @monthly is 0 0 1 * *, @weekly is 0 0 * * 0, @daily (or @midnight) is 0 0 * * * and @hourly is 0 * * * *. @reboot runs once when the cron daemon starts, so it has no schedule to explain.

Why does an expression like 0 0 30 2 * say “never runs”?

February never has a 30th day, so no date matches. The tool searches the next 100 years, skipping whole months and days that cannot match, and says “never runs” when it finds nothing. A schedule on 29 February, by contrast, is valid and runs only in leap years: 0 0 29 2 * runs every four years (except across a century year that is not a leap year, such as 2100).

Which time zone do the run times use?

Cron runs jobs in the time zone of the machine (or the CRON_TZ setting in some versions), which on many servers is UTC. The list shows the times in your device’s zone by default and in UTC when you switch. Around a daylight saving change the tool lists a time that the clocks skip as not run and a time they repeat once; real cron daemons handle those hours in slightly different ways, so avoid scheduling jobs between 01:00 and 03:00 local time on a zone that changes.

Does it support six fields, seconds, L, W, # or ?

No. This tool reads standard five-field cron as used by crontab. Quartz, Spring and AWS EventBridge expressions have a seconds or year field and extra symbols (?, L, W, #) that standard cron does not have, and the tool says so when it sees them.

Is anything I paste sent to a server?

No. The expression is read and the run times are worked out in your browser. The page counts only that the tool was used, never what you typed.