Question 1

Does this support 6-field (seconds) and 7-field (Quartz year) cron?

Accepted Answer

Yes. The parser counts whitespace-separated tokens — exactly
5 means classic POSIX (`min hour dom mon dow`), 6 prepends
a seconds field (`sec min hour dom mon dow`, used by some
BusyBox builds and a few app schedulers), and 7 appends a
year field (`sec min hour dom mon dow year`, the Quartz /
Spring convention). The detected mode shows above the
explanation so you can sanity-check that the line you
pasted is being interpreted the way the system that runs
it will. Range, step (`*/N`), list (`a,b,c`), and range-
with-step (`0-30/5`) all work in every field.

Question 2

What does "this expression will never fire" mean?

Accepted Answer

It means the calendar day you asked for doesn't exist
inside the months you allowed. `0 0 31 2 *` requests
midnight on February 31st — February tops out at 29 — so
a real cron daemon would silently never run this line. We
surface that as a hard error instead of returning an empty
next-runs list. The same logic catches `0 0 31 4,6,9,11 *`
(April/June/September/November all have 30 days) and warns
on `0 0 30 2 *` because it only fires in leap years. Better
to learn this from a tool in two seconds than from a
production page in two weeks.

Question 3

Why a 24×60 grid heatmap instead of just a calendar?

Accepted Answer

Because the question people actually ask is "is my schedule
dense or sparse, and when in the day does it hit?" — and
that's a function of two fields (hour and minute). A 24×60
grid paints exactly the (hour, minute) pairs an expression
will hit on a day where the day-of-month, month, and
day-of-week filters are all satisfied, so you can see at
a glance that `*/7 * * * *` makes a diagonal staircase
instead of clean rows (because 60 isn't divisible by 7),
or that `0 9-17 * * *` is a tidy nine-cell row at the
top of each business hour. A calendar would tell you
which days; the grid tells you the texture of the day
itself.

Question 4

Which timezone are the "next 20 runs" computed in?

Accepted Answer

Your browser's local timezone — the same one cron on your
machine would use. The displayed times include the weekday
in parentheses (Mon/Tue/…) and the delta from the previous
run, so an expression like `0 9-17 * * 1-5` visibly shows
1-hour gaps Mon–Fri and a 64-hour jump across the weekend.
If you need to convert into a different zone, paste the
first fire time into our Timezone Converter — the explainer
itself stays local so you never wonder "is this UTC or my
time?".

Question 5

How is this different from Crontab Helper?

Accepted Answer

Crontab Helper is the *visual builder*: five panels, click
to set "every", "every N", "specific", or "range", and the
expression appears as output. This Explainer is the *reverse*:
paste an expression and we decode it. Use Crontab Helper when
you're writing a schedule from scratch and want guardrails;
use this when you opened a 5-year-old `/etc/crontab` and need
to know what `15 2 * * 0` does before you delete it. Both
link to each other in the footer — pick the right side of
the workflow.

Cron Expression Explainer — Paste, Decode, Preview Next 20 Runs

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Cron Expression Explainer — Decode Any Cron + Next 20 Runs fits into your work

Conversion jobs

Conversion checks

Good next steps

FAQ

Tool combos

Cron Expression Explainer — Paste, Decode, Preview Next 20 Runs

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Cron Expression Explainer — Decode Any Cron + Next 20 Runs fits into your work

Conversion jobs

Conversion checks

Good next steps

FAQ

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