Does this support 6-field cron (with seconds)?

No — only the classic 5-field POSIX cron used by /etc/crontab and Linux/macOS user crontabs. Six-field variants (Quartz, Spring, BusyBox in some builds) add a leading seconds field and a trailing year field, and the syntax for day-of-week differs (0–6 vs 1–7). Mixing them up silently shifts schedules. If you need Quartz, use a Quartz-specific tool — the rules are different enough that one UI can't honestly cover both.

What's the difference between `* * * * 1` (Monday) and `* * 1 * *` (1st of the month)?

Field position. The fifth field is day-of-week (0 = Sunday … 6 = Saturday, with 7 also meaning Sunday on most implementations) and the third field is day-of-month (1–31). `* * * * 1` fires every minute, all day, every Monday — about 1,440 runs per Monday. `* * 1 * *` fires every minute, all day, only on the 1st of each calendar month. When both day-of-month and day-of-week are set (neither is `*`), Vixie cron — the most common implementation — treats it as "OR", which surprises people.

Will cron still fire if my laptop is asleep at the scheduled time?

On Linux servers, classic cron will not catch up missed jobs (anacron does, if installed and configured). On macOS, launchd is what actually runs your "cron" lines, and it has the `StartCalendarInterval` + missed-run replay behavior built in for jobs added via launchctl, but `crontab -e` entries still go through legacy cron which does not replay. The safe pattern for laptops: use launchd directly, or use systemd timers with `Persistent=true` on Linux, both of which replay a missed run on wake.

What's the smallest interval cron actually supports?

One minute. The minute field is the finest grain — `* * * * *` fires every minute. To run more often than once a minute you need a different scheduler (a sleeping loop in your process, systemd timer with `AccuracySec=1s`, or a job queue with a fast tick). Note: even at `* * * * *`, cron's wakeup is not millisecond-precise; jobs typically start within the first 1–2 seconds of the minute.

Why does `*/5` in the hour field skip the way I expect, but `*/7` doesn't?

Step values count from the start of the field's range, not in a rolling way. In the hour field (0–23), `*/5` means 0, 5, 10, 15, 20 — then it resets at midnight, so the gap from 20:00 to the next fire at 00:00 is 4 hours, not 5. `*/7` gives 0, 7, 14, 21, then a 3-hour gap to 00:00. Cron does not carry the remainder across the day boundary. If you need an even 5-hour cadence around the clock, you can't express it in one field — list the hours explicitly (`0,5,10,15,20`) and accept the wrap, or use a systemd timer with `OnUnitActiveSec=5h`.

Set a backup job to run every weekday at 2 AM without re-reading the man page

You need a database dump every business day at 02:00. From memory you might write `0 2 * * 1,5` and accidentally hit only Monday and Friday. Click "specific" minute 0, "specific" hour 2, leave day-of-month "every", and pick the Mon–Fri range on day-of-week. The line reads `0 2 * * 1-5`, the explainer confirms "At 02:00, Monday through Friday", and the next-5 preview shows five consecutive weekday 2 AMs, so you catch a wrong field before it ships.

Inherit a legacy crontab line and figure out what it actually does

A handover doc has `*/15 9-17 * * 1-5` and nobody remembers the intent. Paste it in: the panels light up to every-15-minutes, hours 9 through 17, weekdays, and the plain-English line says "Every 15 minutes, 9 AM to 5 PM, Monday through Friday" — about 36 runs per workday. Now you can see it stops firing at 17:00 (so 17:15 never runs) and decide whether to extend the range to `9-17` plus a trailing `0 18`.

Stop a job from hammering the server at the top of every hour

Three cron jobs all written `0 * * * *` pile up at minute 0 and spike load. Spread them out: give one `7 * * * *`, another `23 * * * *`, a third `41 * * * *`. The builder lets you set a "specific" minute fast, and the next-run preview confirms each lands at a different offset, so you flatten the once-an-hour stampede without touching the hour field.

Schedule a monthly invoice run on the 1st and double-check timezone drift

Finance wants invoices generated 1st of the month at 6 AM. You write `0 6 1 * *`. The next-5 preview is computed in your local clock, so if your server runs UTC and you're in UTC+8, you immediately see the runs land at what looks like 14:00 to you — a hint to either set the hour to `22` the day before or run the job under `TZ=Asia/Shanghai`, instead of discovering the eight-hour gap after the first wrong invoice.

Crontab Helper — Build, Explain & Preview Cron Expressions

Visual crontab builder + human-readable explanation + next run preview.

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

Expression

Explanation

Every 5 minutes

Next 5 runs (local time)

2026-07-02 16:35
2026-07-02 16:40
2026-07-02 16:45
2026-07-02 16:50
2026-07-02 16:55

Presets

Minute

Every

Hour

Day of month

Month

Day of week

What this tool does

Build cron expressions without remembering the field order. Five side-by-side panels (minute, hour, day-of-month, month, day-of-week) each offer the four real-world patterns: "every", "every N", "specific values", and "range". The expression updates as you click, with a plain-English explanation under it ("Every 4 hours, at minute 0") and the next five firing times computed for your local clock. Paste an existing line like `*/15 9-17 * * 1-5` and the UI parses it straight back into the panels so you can edit visually. Eight named presets cover the patterns people actually write — hourly, daily at 3 AM, every weekday business hours, monthly on the first, etc. All math runs in the tab; nothing is sent anywhere.

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 + Preview; 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 <= 20 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 Crontab Helper — Visual Builder & Explainer 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

Set a backup job to run every weekday at 2 AM without re-reading the man page
You need a database dump every business day at 02:00. From memory you might write `0 2 * * 1,5` and accidentally hit only Monday and Friday. Click "specific" minute 0, "specific" hour 2, leave day-of-month "every", and pick the Mon–Fri range on day-of-week. The line reads `0 2 * * 1-5`, the explainer confirms "At 02:00, Monday through Friday", and the next-5 preview shows five consecutive weekday 2 AMs, so you catch a wrong field before it ships.
Inherit a legacy crontab line and figure out what it actually does
A handover doc has `*/15 9-17 * * 1-5` and nobody remembers the intent. Paste it in: the panels light up to every-15-minutes, hours 9 through 17, weekdays, and the plain-English line says "Every 15 minutes, 9 AM to 5 PM, Monday through Friday" — about 36 runs per workday. Now you can see it stops firing at 17:00 (so 17:15 never runs) and decide whether to extend the range to `9-17` plus a trailing `0 18`.
Stop a job from hammering the server at the top of every hour
Three cron jobs all written `0 * * * *` pile up at minute 0 and spike load. Spread them out: give one `7 * * * *`, another `23 * * * *`, a third `41 * * * *`. The builder lets you set a "specific" minute fast, and the next-run preview confirms each lands at a different offset, so you flatten the once-an-hour stampede without touching the hour field.
Schedule a monthly invoice run on the 1st and double-check timezone drift
Finance wants invoices generated 1st of the month at 6 AM. You write `0 6 1 * *`. The next-5 preview is computed in your local clock, so if your server runs UTC and you're in UTC+8, you immediately see the runs land at what looks like 14:00 to you — a hint to either set the hour to `22` the day before or run the job under `TZ=Asia/Shanghai`, instead of discovering the eight-hour gap after the first wrong invoice.

Common pitfalls

Writing `0 2 * * 1,5` when you meant every weekday — commas list specific days (Mon and Fri only), a hyphen `1-5` is the Mon–Fri range. The explainer line tells you which one you actually built.
Assuming `0 0 31 * *` runs every month — months with 30, 28, or 29 days simply skip it. For "last day of month" use a different approach (e.g. `0 0 28-31 * *` with a guard in the script), because plain cron has no L token.
Setting both day-of-month and day-of-week (e.g. `0 0 13 * 5`) and expecting "Friday the 13th" — Vixie cron treats them as OR, so this fires every 13th AND every Friday. Leave one field as `*` unless you truly want the union.

Privacy

Everything runs in your browser tab. Your cron expression, the parsed fields, the explanation, and the next-run times are computed locally in JavaScript with no network call — nothing is sent to a server or logged. The expression you build is written into the page URL so you can bookmark or share a link, so avoid putting secrets in a cron line (you shouldn't anyway — put credentials in the script the job calls, not in crontab).

FAQ

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Crontab Helper — Build, Explain & Preview Cron Expressions

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Crontab Helper — Visual Builder & Explainer fits into your work

Conversion jobs

Conversion checks

Good next steps

Real-world use cases

Set a backup job to run every weekday at 2 AM without re-reading the man page

Inherit a legacy crontab line and figure out what it actually does

Stop a job from hammering the server at the top of every hour

Schedule a monthly invoice run on the 1st and double-check timezone drift

Common pitfalls

Privacy

FAQ

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