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

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.

What does "this expression will never fire" mean?

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.

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

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.

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

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?".

How is this different from Crontab Helper?

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.

Decoding a legacy crontab line before deleting it

You inherit a server and find `15 2 * * 0` in /etc/crontab with no comment. Paste it here and read "at 02:15 on Sunday" plus the next 20 fire times, each tagged with the weekday. Now you know it is the weekly Sunday backup, not a daily job, so you move it to maintenance windows instead of accidentally killing the only off-site backup the team has.

Verifying a step expression fires evenly

A teammate writes `*/7 * * * *` expecting "every 7 minutes, evenly." The 24x60 heatmap shows a diagonal staircase: it fires at :00, :07, :14 ... :56, then jumps back to :00 of the next hour with only a 4-minute gap. You spot the uneven boundary in two seconds and switch to `0,15,30,45 * * * *` for the clean 15-minute cadence the alert pipeline actually needed.

Catching a schedule that never runs

During a code review someone proposes `0 0 31 2 *` for an end-of-month report. Paste it and the never-fires detector flags that February has no 31st, so a real cron daemon would run it zero times all year. You replace it with `0 0 L 2 *` style logic (or `0 0 28 2 *`) before the missing report becomes a quarterly audit finding instead of a one-line fix.

Translating an ops doc across languages

An on-call doc written in Chinese lists `0 9-17 * * 1-5` with a Chinese description. You need to drop the same line into an English runbook for a new hire. The side-by-side English plus Chinese sentence gives you "every hour from 09:00 to 17:00, Monday through Friday" instantly, and the 64-hour weekend gap in the run list confirms it skips Saturday and Sunday as intended.

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

Cron expression explainer — paste any cron, get plain English/Chinese + next 20 runs + visual time grid.

Runs locally
Category Format Converter
Best for Turning pasted content or local files into a handoff-friendly format.

Cron expression

Detected: 5-field POSIX

Plain English

At minutes 0,5,10,15,20,25,30,35,40,45,50,55 during hours 9,10,11,12,13,14,15,16,17, on Mon,Tue,Wed,Thu,Fri

Chinese

在第 9、10、11、12、13、14、15、16、17 小时的第 0、5、10、15、20、25、30、35、40、45、50、55 分，周一、周二、周三、周四、周五

Next 20 runs (local time)

1. 2026-07-02 16:35 (Thu)
2. 2026-07-02 16:40 (Thu)Δ 5m
3. 2026-07-02 16:45 (Thu)Δ 5m
4. 2026-07-02 16:50 (Thu)Δ 5m
5. 2026-07-02 16:55 (Thu)Δ 5m
6. 2026-07-02 17:00 (Thu)Δ 5m
7. 2026-07-02 17:05 (Thu)Δ 5m
8. 2026-07-02 17:10 (Thu)Δ 5m
9. 2026-07-02 17:15 (Thu)Δ 5m
10. 2026-07-02 17:20 (Thu)Δ 5m
11. 2026-07-02 17:25 (Thu)Δ 5m
12. 2026-07-02 17:30 (Thu)Δ 5m
13. 2026-07-02 17:35 (Thu)Δ 5m
14. 2026-07-02 17:40 (Thu)Δ 5m
15. 2026-07-02 17:45 (Thu)Δ 5m
16. 2026-07-02 17:50 (Thu)Δ 5m
17. 2026-07-02 17:55 (Thu)Δ 5m
18. 2026-07-03 09:00 (Fri)Δ 15h
19. 2026-07-03 09:05 (Fri)Δ 5m
20. 2026-07-03 09:10 (Fri)Δ 5m

24h × 60min heatmap (a fire-eligible day)

Each cell = (hour, minute) the schedule hits when all day/month/weekday filters allow.

Common presets

What this tool does

Paste any cron line and get back what it actually does. Five-field POSIX (classic Linux), six-field with seconds (BusyBox, some app schedulers), or seven-field with year (Quartz / Spring) are all auto-detected by counting whitespace-separated tokens — no flavour toggle to forget. Three things show up under the input the moment it parses: a side-by-side English + Chinese sentence explanation so you can paste from a Chinese ops doc and ship the line into an English Slack, the next 20 concrete fire times in your local timezone (with weekday in parentheses and the gap from the previous run, so a "weekdays 9-17" line visibly skips Saturday and Sunday), and a 24-hour × 60-minute heatmap that paints exactly which (hour, minute) cells the expression hits — invaluable for eyeballing whether `*/7 * * * *` really fires evenly or drifts after every hour boundary. The killer feature is the "never fires" detector: write `0 0 31 2 *` and we tell you February has no 31st instead of silently returning no runs; write `0 0 30 2 *` and we explain it only fires in leap years; write `0 0 * * 7,8` and we flag that 8 is not a valid weekday. Twelve presets cover every real schedule (every minute, every five minutes, every fifteen, hourly, every four hours, daily 3 AM, weekday business hours, weekend midnight, monthly on the 1st, quarterly, yearly New Year, last hour of every weekday). Where Crontab Helper is the visual builder you click through, this is the reverse — paste-first, explanation-first, debugger-first. All parsing runs in your tab; expressions are never uploaded.

Tool details

Input: Text + Numbers + Structured content; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: No account required; Open the page and use it; whether results survive refresh depends on the tool.
Performance budget: Initial JS <= 18 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Format Converter · Developer; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

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

Use it when the main problem is getting content from one practical format into another.

Conversion jobs

Turning pasted content or local files into a handoff-friendly format.
Previewing a conversion before you use it in a larger workflow.
Cleaning small format mismatches without opening a full editor.

Conversion checks

Try a small sample first when the source format is messy.
Check character encoding, separators, and line endings after conversion.
Keep the source until the converted output has been reviewed.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Decoding a legacy crontab line before deleting it
You inherit a server and find `15 2 * * 0` in /etc/crontab with no comment. Paste it here and read "at 02:15 on Sunday" plus the next 20 fire times, each tagged with the weekday. Now you know it is the weekly Sunday backup, not a daily job, so you move it to maintenance windows instead of accidentally killing the only off-site backup the team has.
Verifying a step expression fires evenly
A teammate writes `*/7 * * * *` expecting "every 7 minutes, evenly." The 24x60 heatmap shows a diagonal staircase: it fires at :00, :07, :14 ... :56, then jumps back to :00 of the next hour with only a 4-minute gap. You spot the uneven boundary in two seconds and switch to `0,15,30,45 * * * *` for the clean 15-minute cadence the alert pipeline actually needed.
Catching a schedule that never runs
During a code review someone proposes `0 0 31 2 *` for an end-of-month report. Paste it and the never-fires detector flags that February has no 31st, so a real cron daemon would run it zero times all year. You replace it with `0 0 L 2 *` style logic (or `0 0 28 2 *`) before the missing report becomes a quarterly audit finding instead of a one-line fix.
Translating an ops doc across languages
An on-call doc written in Chinese lists `0 9-17 * * 1-5` with a Chinese description. You need to drop the same line into an English runbook for a new hire. The side-by-side English plus Chinese sentence gives you "every hour from 09:00 to 17:00, Monday through Friday" instantly, and the 64-hour weekend gap in the run list confirms it skips Saturday and Sunday as intended.

Common pitfalls

Confusing day-of-month and day-of-week — `0 0 * * 1` means every Monday, not the 1st of the month; for the 1st use `0 0 1 * *`. Paste both and compare the run lists to be sure.
Assuming `*/N` always fits the hour — `*/7 * * * *` does not divide 60 evenly, so it drifts at each hour boundary. Check the heatmap before trusting an even cadence.
Forgetting the field count your runner expects — pasting a 6-field seconds expression into a 5-field POSIX daemon shifts every field left. Confirm the detected mode (5 vs 6 vs 7) matches the system that runs it.

Privacy

Every step — token counting, mode detection, the next-20-runs computation, and the heatmap — runs entirely in your browser tab. Your cron expressions are never uploaded or logged. The expression is stored in the page URL so you can share or bookmark a decoded result; if your cron line is sensitive, clear the input before copying the link.

FAQ

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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

Real-world use cases

Decoding a legacy crontab line before deleting it

Verifying a step expression fires evenly

Catching a schedule that never runs

Translating an ops doc across languages

Common pitfalls

Privacy

FAQ

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