Cron Expression Parser & Generator

Two modes in one tool: build a schedule by picking a frequency and never touch the five-field syntax, or paste an existing expression and get a plain-English description, a field breakdown, and the next five run times in your local timezone.

Build mode — no syntax required

Plain-English description

Next 5 run times, local timezone

Field-by-field breakdown

Ranges, steps, lists and name aliases

Detects 6-field Quartz expressions

How to build or read a cron expression

Pick Build or Parse

Use Build if you are starting from scratch and want to pick a frequency without touching the five-field syntax. Use Parse if you already have an expression and need it explained.

Build: choose a frequency

Pick minutes, hours, daily, weekly or monthly, then fill in the time — the tool writes the correct expression as you go.

Parse: paste the expression

Enter the five-field schedule, for example 30 3 * * 1-5. Shortcuts like @daily or @weekly work too.

Check the next run times

Either mode shows the same plain-English description and the next five executions, computed in your browser timezone.

Build mode versus Parse mode#

Build mode exists because the five-field syntax is genuinely unintuitive the first several times — remembering that minute comes before hour, or that */4 in the hour field does not mean "every 4th hour starting from now," is friction that has nothing to do with what you actually want, which is usually "run this at 3am" or "run this every 15 minutes."

Under the hood, Build mode just writes a normal five-field expression and hands it to the exact same parser Parse mode uses — the description, the field breakdown and the next-run times you see are identical either way. Build it visually, then switch to Parse mode any time to see the raw expression it produced.

The five fields, in order#

A crontab line is five space-separated fields: minute hour day-of-month month day-of-week. Minutes run 0–59, hours 0–23, day of month 1–31, month 1–12, and day of week 0–6 where 0 is Sunday. Most implementations also accept 7 for Sunday, and three-letter names like MON or JAN.

Each field accepts four things: a single value (5), a list (1,15,30), a range (1-5) and a step (*/15, or 0-30/5 for every five minutes in the first half hour). An asterisk means "every value".

The day-of-month and day-of-week trap#

This is the single most misunderstood part of cron. When both the day-of-month and the day-of-week fields are restricted, cron combines them with OR, not AND. So 0 0 13 * 5 does not mean "Friday the 13th" — it means "midnight on the 13th of every month, and also every Friday".

Getting a true "Friday the 13th" schedule requires a day-of-month check inside the job itself. When exactly one of the two fields is restricted, the behaviour is the intuitive one, which is why the bug hides for so long.

Timezones, and why the run times here may not match your server#

The next run times shown on this page are computed in your browser's timezone. Your server almost certainly runs cron in UTC, or in whatever the system timezone happens to be. A daily job at 0 2 * * * fires at 02:00 server time, which may be a completely different hour where you are.

Daylight saving time makes it worse. When the clock jumps forward, jobs scheduled inside the skipped hour may not run at all that day; when it falls back, they can run twice. If a job must not be skipped or duplicated, schedule it in UTC or make it idempotent.

Standard cron, Quartz and the seconds field#

Classic Unix crontab has five fields and a one-minute resolution — you cannot schedule anything more frequent than once per minute. Quartz, Spring's @Scheduled, and several job libraries add a seconds field at the front, making six.

If you paste a six-field expression here, the tool tells you rather than guessing, because the same string means different schedules in the two dialects. Some Quartz expressions also use ?, L and #, which standard crontab does not understand.

Frequently asked questions

Do I need to know the cron syntax to use this tool?

No — Build mode lets you pick a frequency (every N minutes, daily, weekly on specific days, monthly on a specific day) from a form, and it writes the five-field expression for you. Switch to Parse mode any time to see the exact expression it generated.

What does */15 mean in a cron expression?

It is a step value: every 15 units within the field, starting from the lowest allowed value. In the minute field, */15 means minutes 0, 15, 30 and 45 of every hour. Note that it steps from the start of the field, not from the current time.

Are the run times shown in UTC or my local time?

Your local time, taken from your browser. Servers usually run cron in UTC or the system timezone, so compare carefully before assuming a job will fire when this page says it will.

Why does my expression run more often than I expected?

The most common cause is setting both the day-of-month and the day-of-week fields. Cron treats them as OR when both are restricted, so the job runs on either condition. Leave one of them as an asterisk unless you genuinely want both.

Can cron run a job every 30 seconds?

Not with standard crontab, which has a resolution of one minute. The usual workarounds are two entries with a sleep offset, a systemd timer, or a scheduler like Quartz that supports a seconds field.

What is the difference between @daily and 0 0 * * *?

Nothing — @daily is a shorthand that expands to exactly 0 0 * * *. The other shortcuts are @hourly, @weekly, @monthly and @yearly. @reboot is different: it runs once at startup and has no recurring schedule.

Does day of week start at 0 or 1?

0 is Sunday in standard cron, running through 6 for Saturday. Most implementations also accept 7 as Sunday. Three-letter names like SUN, MON and FRI work too and are far easier to read.

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