ตัวอธิบาย Cron Expression

(เอกสารเป็นภาษาอังกฤษ)

What it does

The Cron Expression Explainer reads any standard 5-field cron expression and translates it into plain English. Type (or pick) an expression and the right-hand panel shows a one-line summary, a field-by-field table of what each part matches, and the next five times it will fire with relative offsets (“in 6 hours”) — all evaluated in UTC so results are unambiguous and DST-independent. Flip to Build mode and it composes an expression field-by-field from friendly inputs. Everything runs 100% in your browser, so internal schedules never leave your machine.

How to use it

1. Pick one of the Common chips (* * * * *, 0 0 * * *, 0 9 * * 1, 0 0 1 * *, 0 */6 * * *) or type a 5-field expression into Cron expression (or hit Sample for 30 9 * * MON-FRI).
2. Read the plain-English summary, the per-field table, and the Upcoming runs list on the right.
3. Switch to Build and fill the five fields (minute, hour, day-of-month, month, day-of-week) to assemble an expression you can copy.
4. Use Copy share link (in Explain mode) to reproduce the exact view — the expression is encoded in the URL.

Field cheat sheet

#	Field	Allowed values	Names	Specials
1	minute	0–59	—	* any · , list · - range · / step
2	hour	0–23	—	* · , · - · /
3	day of month	1–31	—	* · , · - · /
4	month	1–12	JAN–DEC	* · , · - · /
5	day of week	0–7 (0 and 7 = Sunday)	SUN–SAT	* · , · - · /

Step syntax works in all three forms: */15 (from the field minimum), 0-30/10 (range step), 5/10 (from 5 to the field maximum). When both day-of-month and day-of-week are restricted, a match on either suffices (standard Vixie-cron behavior). Not supported: Quartz extensions (?, L, W, #), 6-field seconds syntax, and @reboot-style macros.

Examples

Verified against the tool’s parser:

Expression	Explanation
* * * * *	Every minute
0 0 * * *	At 00:00
0 9 * * 1	At 09:00, on Monday
0 0 1 * *	At 00:00, on day 1 of the month
0 */6 * * *	Every 6 hours, minute 0
30 9 * * MON-FRI	At 09:30, on Monday through Friday
*/15 * * * *	Every 15 minutes
0 0 1,15 * *	At 00:00, on days 1, 15 of the month
5 4 * * SUN	At 04:05, on Sunday
0 12 */2 * *	At 12:00, every 2 days of the month
0 0 * 6 SAT	At 00:00, in June, on Saturday
23 0-20/2 * * *	Every 2 hours, minute 23

Upcoming runs. For 30 9 * * MON-FRI evaluated from Wednesday 2026-08-26 12:00 UTC, the next three firings are Aug 27, Aug 28, and Aug 31 at 09:30 UTC (it skips the weekend).

Invalid input. 99 * * * (four fields) reports Expected 5 fields (minute hour day-of-month month day-of-week), got 4 in the error panel. 99 * * * * reports minute: value 99 is above maximum 59. 0 0 31 2 * is grammatically valid but February has no 31st — the panel shows “No upcoming run within ~3 years”.

Good to know

• Shareable: in Explain mode your expression is encoded in the URL, so a link reproduces the exact explanation.
• Private: all parsing happens locally — safe for internal or proprietary schedules.
• Times are UTC. The upcoming runs assume the schedule runs on UTC clocks. Most servers run crond on local machine time, so shift accordingly before trusting the countdown.
• Five upcoming firings are listed, searched up to ~3 years ahead; an expression that never matches a real date (like Feb 31) shows the empty note instead.
• Related tools: JSON → TypeScript, JSON Formatter,

  Base64Base64An encoding representing binary data as 64 safe ASCII characters, so it survives transport through text-only channels. It encodes — it does not encrypt.

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