Cron Expression Generator

Five-field Unix cron

Classic cron uses five fields: minute, hour, day of month, month, day of week. This page helps you assemble those fields and preview upcoming runs in local browser time using a simple expander for common patterns.

Naming differs on some platforms (Quartz adds seconds). Confirm whether your scheduler wants five fields or six before you paste.

Worked example: reading three common expressions

0 9 * * 1-5 means 09:00 every weekday. */15 * * * * means every 15 minutes. 30 2 1 * * means 02:30 on the first day of each month.

When both day-of-month and day-of-week are restricted, Unix cron treats that as OR on many systems. Read your scheduler docs; behavior is a common source of surprises.

Limits

Next-run previews are best-effort in the browser and ignore DST edge cases some engines special-case. This tool does not install crontab entries or talk to servers.

Worked schedules you can reuse

15 6 * * 1-5 is 06:15 on weekdays. 0 0 1 1 * is midnight on January 1. 0 */6 * * * is every six hours on the hour. 30 2 * * 0 is 02:30 every Sunday. Write the human sentence next to the expression in your runbook so the next on-call engineer does not reverse the fields.

Field order from left to right is minute, hour, day of month, month, and day of week. Mixing up hour and minute is the most common paste error when copying from dashboards that show human clocks first.

Pitfalls

• Time zone. Cron runs in the server's time zone, often UTC. 6 AM UTC is not 6 AM in your city.
• Day of month and day of week together. In standard cron, if both are restricted the job runs when either matches, not both.
• Daylight saving. Jobs scheduled between 1 and 3 AM local time can be skipped or run twice on clock-change days.
• Five vs six fields. Quartz and some platforms add a seconds field. Check what your scheduler expects.

Parse cron and list next runs in code

Each snippet parses the 5-field expression */15 9-17 * * 1-5 (every 15 minutes, 9:00 to 17:45, Monday to Friday) and prints the next three runs in a named time zone.

JavaScript: cron-parser (v5)

import { CronExpressionParser } from "cron-parser"; // npm i cron-parser (v5)

const interval = CronExpressionParser.parse("*/15 9-17 * * 1-5", {
  tz: "America/Los_Angeles", // cron has no time zone of its own
});
for (let i = 0; i < 3; i++) console.log(interval.next().toISOString());

Python: croniter

from datetime import datetime
from zoneinfo import ZoneInfo
from croniter import croniter  # pip install croniter

start = datetime.now(ZoneInfo("America/Los_Angeles"))
it = croniter("*/15 9-17 * * 1-5", start)
for _ in range(3):
    print(it.get_next(datetime).isoformat())

print(croniter.is_valid("61 * * * *"))  # False: minute is 0-59

Go: github.com/robfig/cron/v3

package main

import (
	"fmt"
	"time"

	"github.com/robfig/cron/v3" // go get github.com/robfig/cron/v3
)

func main() {
	sched, err := cron.ParseStandard("*/15 9-17 * * 1-5") // 5-field Unix syntax
	if err != nil {
		panic(err)
	}
	loc, _ := time.LoadLocation("America/Los_Angeles")
	t := time.Now().In(loc)
	for i := 0; i < 3; i++ {
		t = sched.Next(t)
		fmt.Println(t.Format(time.RFC3339))
	}
}

Each snippet was run on October 14, 2026 with cron-parser 5.10.2, croniter 6.2.4 and robfig/cron v3.0.1.

Cron syntax references

• POSIX: crontab: the five fields and their ranges
• crontab(5) Linux manual page: step values, names like mon, and the day-of-month or day-of-week rule
• cron-parser (JavaScript)
• croniter (Python)
• Go: robfig/cron v3

FAQ