What's the difference between 5-field and 6-field cron?

Standard POSIX cron uses 5 fields starting at the minute. Quartz, Spring, and some cloud schedulers prepend a seconds field for 6 total. The builder lets you switch modes so the expression matches your scheduler.

How do day-of-month and day-of-week interact?

In standard cron the two fields are OR-ed: if either matches, the job fires. Set one to * when you only want the other to constrain firing.

The step operator. */15 in the minute field fires every 15 minutes starting at 0. 5/15 fires at minute 5, 20, 35, 50. Steps work in any field.

Is the cron expression sent anywhere?

No. Parsing and the next-run preview are computed locally in your browser. Nothing is logged or transmitted.

5 fields · visual builder · next runs · live

Build a cron expression

Compose the five classic cron fields with quick-pick presets. Live human-readable description and the next five fire times update as you type.

Cron Builder

Expression

0 9 * * 1-5

5 fields

Description

Runs at minute 0, hour 9, on every day o…

humanized

Next runs

previewed

Mode

live

client

Expression0 9 * * 1-5

input · fields

Minute (0–59)

Hour (0–23)

Day of month

Month (1–12)

Weekday (0=Sun)

output · preview

0 9 * * 1-5

Runs at minute 0, hour 9, on every day of every month, weekday 1,2,3,4,5.

Next runs

Mon Sep 28 2026 09:00:00 GMT+0000 (Coordinated Universal Time)
Tue Sep 29 2026 09:00:00 GMT+0000 (Coordinated Universal Time)
Wed Sep 30 2026 09:00:00 GMT+0000 (Coordinated Universal Time)
Thu Oct 01 2026 09:00:00 GMT+0000 (Coordinated Universal Time)
Fri Oct 02 2026 09:00:00 GMT+0000 (Coordinated Universal Time)

Quick Start

How cron expressions work

Five space-separated fields: minute, hour, day-of-month, month, day-of-week. Use * for any, */N for steps, A-B for ranges, A,B for lists.

01
Pick each field
Start coarse — once a day at 9am means 0 9.
Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.
inputISO 8601RFC 3339epochlive
field · timestampminute · ISO
```
0 9 * * *
```
loaded · ISO 8601zone · ready
02
Use presets
Click * or */5 to drop in common values.
All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.
presetUTC mathIntlDST-safelive
preset · options*/5 · live
```
*/5 every 5 min
```
options applied · UTCDST-safe
03
Restrict by weekday
1-5 = Mon–Fri. 0,6 = weekends.
Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.
weekdayoffsetzone-awaresortablepadded
dow · computed1-5 · ready
```
Mon–Fri only
```
computed · instantsortable
04
Preview the schedule
The next five fire times appear immediately — sanity-check before deploying.
Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.
previewclipboardno oracledeterministicclient-side
✓ · copiedready · done
```
Mon 09:00 …
```
shipped · ready to shipsuccess

Pro tips

Time math without DST landmines

Always store UTC

Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.

Watch leap seconds

POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.

Prefer Temporal eventually

The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.

Cron is timezone-tricky

Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.

ISO 8601 sorts naturally

YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.

Beware Y2K38

Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.

Use Cases

When to build cron expressions

Servers, schedulers, CI jobs.

Linux crontab

Tune backup or log-rotate jobs without trial-and-error. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.

DST-safe

Kubernetes CronJob

Author schedule strings for k8s manifests safely. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.

k8s

GitHub Actions

Pick exact UTC times for scheduled workflows. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.

ISO-sortable

node-cron

Translate human schedules into expressions for node-cron or croner. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.

spec-grade

Postgres pg_cron

Drop expressions straight into pg_cron.schedule. Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".

zone-aware

Documentation

Generate readable schedule docs from one source string. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.

epoch-accurate

FAQ

Frequently asked questions

Do seconds get a column?

Classic Unix cron has 5 fields (no seconds). Use Quartz Converter for the 6/7-field flavour.

Which weekday is 0?

Sunday in Unix cron. Some flavours use 1 — check your scheduler's docs.

How are next runs computed?

Iterating minute-by-minute and matching against the expression. Up to five future runs are shown.

Does it handle ranges + steps together?

Yes — try 8-18/2 in the hour field for every two hours from 8 to 18.

Is anything sent to a server?

No. The expression and preview are computed in your browser.

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